From a5f7a5bb3b7f28ba7e4fa246775b29a0e5537255 Mon Sep 17 00:00:00 2001 From: Jinke Han Date: Tue, 8 Sep 2026 15:37:42 +0800 Subject: x86/kprobes: Fix crash when probing CS CALL instructions When using eBPF to probe CS CALL instructions within a function, a crash can be triggered. The eBPF tool probes offset 257 of the __hrtimer_run_queues() function: <__hrtimer_run_queues+249>: nopl 0x0(%rax,%rax,1) <__hrtimer_run_queues+254>: mov %r14,%rdi <__hrtimer_run_queues+257>: cs call <__x86_indirect_thunk_r12> <__hrtimer_run_queues+263>: mov %eax,%r12d <__hrtimer_run_queues+266>: xchg %ax,%ax <__hrtimer_run_queues+268>: mov %r13,%rdi Which triggers this crash: BUG: unable to handle page fault for address: 00000000000f41c9 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 0 P4D 0 Oops: 0002 [#1] SMP NOPTI CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P RIP: 0010:__hrtimer_run_queues+0x106/0x230 Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is at the 6th byte of the above CS CALL instruction. Since the CS CALL instruction occupies 6 bytes, the exception occurred in the middle of that call instruction. The root cause is that when using eBPF tools to probe in the middle of a function, a kprobe with INT3 is used as the underlying implementation. During single-step emulation of the original CALL instruction, int3_emulate_call() assumes that the probed CALL instruction is 5 bytes long. However, the actual CS-prefixed CALL instruction occupies 6 bytes, so it constructs an incorrect exception return address. When the CPU returns from the kprobe handler, the next instruction to be executed is at the address of the last byte of that CS CALL instruction. Coincidentally, starting from that address, the CPU fetches and decodes a completely different instruction, which ultimately triggers a kernel crash. Fix the issue by using the actual instruction length obtained from the instruction decoder when constructing the exception return address, rather than relying on the hardcoded CALL_INSN_SIZE macro. [ mingo: Refined the changelog ] Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step") Suggested-by: Masami Hiramatsu (Google) Signed-off-by: Jinke Han Signed-off-by: Ingo Molnar Reviewed-by: Masami Hiramatsu (Google) Acked-by: Yafang Shao Acked-by: Borislav Petkov Cc: Peter Zijlstra Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000 --- fs/ext4/dir.c | 710 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 710 insertions(+) create mode 100644 fs/ext4/dir.c (limited to 'fs/ext4/dir.c') diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c new file mode 100644 index 000000000..8d7b81e69 --- /dev/null +++ b/fs/ext4/dir.c @@ -0,0 +1,710 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * linux/fs/ext4/dir.c + * + * Copyright (C) 1992, 1993, 1994, 1995 + * Remy Card (card@masi.ibp.fr) + * Laboratoire MASI - Institut Blaise Pascal + * Universite Pierre et Marie Curie (Paris VI) + * + * from + * + * linux/fs/minix/dir.c + * + * Copyright (C) 1991, 1992 Linus Torvalds + * + * ext4 directory handling functions + * + * Big-endian to little-endian byte-swapping/bitmaps by + * David S. Miller (davem@caip.rutgers.edu), 1995 + * + * Hash Tree Directory indexing (c) 2001 Daniel Phillips + * + */ + +#include +#include +#include +#include +#include +#include +#include "ext4.h" +#include "xattr.h" + +static int ext4_dx_readdir(struct file *, struct dir_context *); + +/** + * is_dx_dir() - check if a directory is using htree indexing + * @inode: directory inode + * + * Check if the given dir-inode refers to an htree-indexed directory + * (or a directory which could potentially get converted to use htree + * indexing). + * + * Return 1 if it is a dx dir, 0 if not + */ +static int is_dx_dir(struct inode *inode) +{ + struct super_block *sb = inode->i_sb; + + if (ext4_has_feature_dir_index(inode->i_sb) && + ((ext4_test_inode_flag(inode, EXT4_INODE_INDEX)) || + ((inode->i_size >> sb->s_blocksize_bits) == 1) || + ext4_has_inline_data(inode))) + return 1; + + return 0; +} + +static bool is_fake_dir_entry(struct ext4_dir_entry_2 *de) +{ + /* Check if . or .. , or skip if namelen is 0 */ + if ((de->name_len > 0) && (de->name_len <= 2) && (de->name[0] == '.') && + (de->name[1] == '.' || de->name[1] == '\0')) + return true; + /* Check if this is a csum entry */ + if (de->file_type == EXT4_FT_DIR_CSUM) + return true; + return false; +} + +/* + * Return 0 if the directory entry is OK, and 1 if there is a problem + * + * Note: this is the opposite of what ext2 and ext3 historically returned... + * + * bh passed here can be an inode block or a dir data block, depending + * on the inode inline data flag. + */ +int __ext4_check_dir_entry(const char *function, unsigned int line, + struct inode *dir, struct file *filp, + struct ext4_dir_entry_2 *de, + struct buffer_head *bh, char *buf, int size, + unsigned int offset) +{ + const char *error_msg = NULL; + const int rlen = ext4_rec_len_from_disk(de->rec_len, + dir->i_sb->s_blocksize); + const int next_offset = ((char *) de - buf) + rlen; + bool fake = is_fake_dir_entry(de); + bool has_csum = ext4_has_feature_metadata_csum(dir->i_sb); + + if (unlikely(rlen < ext4_dir_rec_len(1, fake ? NULL : dir))) + error_msg = "rec_len is smaller than minimal"; + else if (unlikely(rlen % 4 != 0)) + error_msg = "rec_len % 4 != 0"; + else if (unlikely(rlen < ext4_dir_rec_len(de->name_len, + fake ? NULL : dir))) + error_msg = "rec_len is too small for name_len"; + else if (unlikely(next_offset > size)) + error_msg = "directory entry overrun"; + else if (unlikely(next_offset > size - ext4_dir_rec_len(1, + has_csum ? NULL : dir) && + next_offset != size)) + error_msg = "directory entry too close to block end"; + else if (unlikely(le32_to_cpu(de->inode) > + le32_to_cpu(EXT4_SB(dir->i_sb)->s_es->s_inodes_count))) + error_msg = "inode out of bounds"; + else if (unlikely(next_offset == size && de->name_len == 1 && + de->name[0] == '.')) + error_msg = "'.' directory cannot be the last in data block"; + else + return 0; + + if (filp) + ext4_error_file(filp, function, line, bh->b_blocknr, + "bad entry in directory: %s - offset=%u, " + "inode=%u, rec_len=%d, size=%d fake=%d", + error_msg, offset, le32_to_cpu(de->inode), + rlen, size, fake); + else + ext4_error_inode(dir, function, line, bh->b_blocknr, + "bad entry in directory: %s - offset=%u, " + "inode=%u, rec_len=%d, size=%d fake=%d", + error_msg, offset, le32_to_cpu(de->inode), + rlen, size, fake); + + return 1; +} + +static int ext4_readdir(struct file *file, struct dir_context *ctx) +{ + unsigned int offset; + int i; + struct ext4_dir_entry_2 *de; + int err; + struct inode *inode = file_inode(file); + struct super_block *sb = inode->i_sb; + struct buffer_head *bh = NULL; + struct fscrypt_str fstr = FSTR_INIT(NULL, 0); + struct dir_private_info *info = file->private_data; + bool has_csum = ext4_has_feature_metadata_csum(sb); + + err = fscrypt_prepare_readdir(inode); + if (err) + return err; + + if (is_dx_dir(inode)) { + err = ext4_dx_readdir(file, ctx); + if (err != ERR_BAD_DX_DIR) + return err; + + /* Can we just clear INDEX flag to ignore htree information? */ + if (!has_csum) { + /* + * We don't set the inode dirty flag since it's not + * critical that it gets flushed back to the disk. + */ + ext4_clear_inode_flag(inode, EXT4_INODE_INDEX); + } + } + + if (ext4_has_inline_data(inode)) { + int has_inline_data = 1; + err = ext4_read_inline_dir(file, ctx, + &has_inline_data); + if (has_inline_data) + return err; + } + + if (IS_ENCRYPTED(inode)) { + err = fscrypt_fname_alloc_buffer(EXT4_NAME_LEN, &fstr); + if (err < 0) + return err; + } + + while (ctx->pos < inode->i_size) { + struct ext4_map_blocks map; + + if (fatal_signal_pending(current)) { + err = -ERESTARTSYS; + goto errout; + } + cond_resched(); + offset = ctx->pos & (sb->s_blocksize - 1); + map.m_lblk = ctx->pos >> EXT4_BLOCK_SIZE_BITS(sb); + map.m_len = 1; + err = ext4_map_blocks(NULL, inode, &map, 0); + if (err == 0) { + /* m_len should never be zero but let's avoid + * an infinite loop if it somehow is */ + if (map.m_len == 0) + map.m_len = 1; + ctx->pos += map.m_len * sb->s_blocksize; + continue; + } + if (err > 0) { + pgoff_t index = map.m_pblk << inode->i_blkbits >> + PAGE_SHIFT; + if (!ra_has_index(&file->f_ra, index)) + page_cache_sync_readahead( + sb->s_bdev->bd_mapping, + &file->f_ra, file, index, + 1 << EXT4_SB(sb)->s_min_folio_order); + file->f_ra.prev_pos = (loff_t)index << PAGE_SHIFT; + bh = ext4_bread(NULL, inode, map.m_lblk, 0); + if (IS_ERR(bh)) { + err = PTR_ERR(bh); + bh = NULL; + goto errout; + } + } + + if (!bh) { + /* corrupt size? Maybe no more blocks to read */ + if (ctx->pos > inode->i_blocks << 9) + break; + ctx->pos += sb->s_blocksize - offset; + continue; + } + + /* Check the checksum */ + if (!buffer_verified(bh) && + !ext4_dirblock_csum_verify(inode, bh)) { + EXT4_ERROR_FILE(file, 0, "directory fails checksum " + "at offset %llu", + (unsigned long long)ctx->pos); + ctx->pos += sb->s_blocksize - offset; + brelse(bh); + bh = NULL; + continue; + } + set_buffer_verified(bh); + + /* If the dir block has changed since the last call to + * readdir(2), then we might be pointing to an invalid + * dirent right now. Scan from the start of the block + * to make sure. */ + if (!inode_eq_iversion(inode, info->cookie)) { + for (i = 0; + i <= sb->s_blocksize - + ext4_dir_rec_len(1, has_csum ? NULL : inode) && + i < offset;) { + de = (struct ext4_dir_entry_2 *) + (bh->b_data + i); + /* It's too expensive to do a full + * dirent test each time round this + * loop, but we do have to test at + * least that it is non-zero. A + * failure will be detected in the + * dirent test below. */ + if (ext4_rec_len_from_disk(de->rec_len, + sb->s_blocksize) < ext4_dir_rec_len(1, + inode)) + break; + i += ext4_rec_len_from_disk(de->rec_len, + sb->s_blocksize); + } + offset = i; + ctx->pos = (ctx->pos & ~(sb->s_blocksize - 1)) + | offset; + info->cookie = inode_query_iversion(inode); + } + + if (unlikely(offset < sb->s_blocksize && + offset > sb->s_blocksize - + ext4_dir_rec_len(1, has_csum ? NULL : inode))) { + EXT4_ERROR_FILE(file, bh->b_blocknr, + "bad entry in directory: %s - offset=%u, size=%lu", + "directory entry too close to block end", + offset, sb->s_blocksize); + ctx->pos = round_up(ctx->pos, sb->s_blocksize); + goto next_block; + } + + while (ctx->pos < inode->i_size + && offset < sb->s_blocksize) { + de = (struct ext4_dir_entry_2 *) (bh->b_data + offset); + if (ext4_check_dir_entry(inode, file, de, bh, + bh->b_data, bh->b_size, + offset)) { + /* + * On error, skip to the next block + */ + ctx->pos = (ctx->pos | + (sb->s_blocksize - 1)) + 1; + break; + } + offset += ext4_rec_len_from_disk(de->rec_len, + sb->s_blocksize); + if (le32_to_cpu(de->inode)) { + if (!IS_ENCRYPTED(inode)) { + if (!dir_emit(ctx, de->name, + de->name_len, + le32_to_cpu(de->inode), + get_dtype(sb, de->file_type))) + goto done; + } else { + int save_len = fstr.len; + struct fscrypt_str de_name = + FSTR_INIT(de->name, + de->name_len); + u32 hash; + u32 minor_hash; + + if (IS_CASEFOLDED(inode)) { + hash = EXT4_DIRENT_HASH(de); + minor_hash = EXT4_DIRENT_MINOR_HASH(de); + } else { + hash = 0; + minor_hash = 0; + } + + /* Directory is encrypted */ + err = fscrypt_fname_disk_to_usr(inode, + hash, minor_hash, &de_name, &fstr); + de_name = fstr; + fstr.len = save_len; + if (err) + goto errout; + if (!dir_emit(ctx, + de_name.name, de_name.len, + le32_to_cpu(de->inode), + get_dtype(sb, de->file_type))) + goto done; + } + } + ctx->pos += ext4_rec_len_from_disk(de->rec_len, + sb->s_blocksize); + } +next_block: + if ((ctx->pos < inode->i_size) && !dir_relax_shared(inode)) + goto done; + brelse(bh); + bh = NULL; + } +done: + err = 0; +errout: + fscrypt_fname_free_buffer(&fstr); + brelse(bh); + return err; +} + +static inline int is_32bit_api(void) +{ +#ifdef CONFIG_COMPAT + return in_compat_syscall(); +#else + return (BITS_PER_LONG == 32); +#endif +} + +/* + * These functions convert from the major/minor hash to an f_pos + * value for dx directories + * + * Upper layer (for example NFS) should specify FMODE_32BITHASH or + * FMODE_64BITHASH explicitly. On the other hand, we allow ext4 to be mounted + * directly on both 32-bit and 64-bit nodes, under such case, neither + * FMODE_32BITHASH nor FMODE_64BITHASH is specified. + */ +static inline loff_t hash2pos(struct file *filp, __u32 major, __u32 minor) +{ + if ((filp->f_mode & FMODE_32BITHASH) || + (!(filp->f_mode & FMODE_64BITHASH) && is_32bit_api())) + return major >> 1; + else + return ((__u64)(major >> 1) << 32) | (__u64)minor; +} + +static inline __u32 pos2maj_hash(struct file *filp, loff_t pos) +{ + if ((filp->f_mode & FMODE_32BITHASH) || + (!(filp->f_mode & FMODE_64BITHASH) && is_32bit_api())) + return (pos << 1) & 0xffffffff; + else + return ((pos >> 32) << 1) & 0xffffffff; +} + +static inline __u32 pos2min_hash(struct file *filp, loff_t pos) +{ + if ((filp->f_mode & FMODE_32BITHASH) || + (!(filp->f_mode & FMODE_64BITHASH) && is_32bit_api())) + return 0; + else + return pos & 0xffffffff; +} + +/* + * Return 32- or 64-bit end-of-file for dx directories + */ +static inline loff_t ext4_get_htree_eof(struct file *filp) +{ + if ((filp->f_mode & FMODE_32BITHASH) || + (!(filp->f_mode & FMODE_64BITHASH) && is_32bit_api())) + return EXT4_HTREE_EOF_32BIT; + else + return EXT4_HTREE_EOF_64BIT; +} + + +/* + * ext4_dir_llseek() calls generic_file_llseek_size to handle htree + * directories, where the "offset" is in terms of the filename hash + * value instead of the byte offset. + * + * Because we may return a 64-bit hash that is well beyond offset limits, + * we need to pass the max hash as the maximum allowable offset in + * the htree directory case. + * + * For non-htree, ext4_llseek already chooses the proper max offset. + */ +static loff_t ext4_dir_llseek(struct file *file, loff_t offset, int whence) +{ + struct inode *inode = file->f_mapping->host; + struct dir_private_info *info = file->private_data; + int dx_dir = is_dx_dir(inode); + loff_t ret, htree_max = ext4_get_htree_eof(file); + + if (likely(dx_dir)) + ret = generic_file_llseek_size(file, offset, whence, + htree_max, htree_max); + else + ret = ext4_llseek(file, offset, whence); + info->cookie = inode_peek_iversion(inode) - 1; + return ret; +} + +/* + * This structure holds the nodes of the red-black tree used to store + * the directory entry in hash order. + */ +struct fname { + __u32 hash; + __u32 minor_hash; + struct rb_node rb_hash; + struct fname *next; + __u32 inode; + __u8 name_len; + __u8 file_type; + char name[] __counted_by(name_len); +}; + +/* + * This function implements a non-recursive way of freeing all of the + * nodes in the red-black tree. + */ +static void free_rb_tree_fname(struct rb_root *root) +{ + struct fname *fname, *next; + + rbtree_postorder_for_each_entry_safe(fname, next, root, rb_hash) + while (fname) { + struct fname *old = fname; + fname = fname->next; + kfree(old); + } + + *root = RB_ROOT; +} + +static void ext4_htree_init_dir_info(struct file *filp, loff_t pos) +{ + struct dir_private_info *p = filp->private_data; + + if (is_dx_dir(file_inode(filp)) && !p->initialized) { + p->curr_hash = pos2maj_hash(filp, pos); + p->curr_minor_hash = pos2min_hash(filp, pos); + p->initialized = true; + } +} + +void ext4_htree_free_dir_info(struct dir_private_info *p) +{ + free_rb_tree_fname(&p->root); + kfree(p); +} + +/* + * Given a directory entry, enter it into the fname rb tree. + * + * When filename encryption is enabled, the dirent will hold the + * encrypted filename, while the htree will hold decrypted filename. + * The decrypted filename is passed in via ent_name. parameter. + */ +int ext4_htree_store_dirent(struct file *dir_file, __u32 hash, + __u32 minor_hash, + struct ext4_dir_entry_2 *dirent, + struct fscrypt_str *ent_name) +{ + struct rb_node **p, *parent = NULL; + struct fname *fname, *new_fn; + struct dir_private_info *info; + + info = dir_file->private_data; + p = &info->root.rb_node; + + /* Create and allocate the fname structure */ + new_fn = kzalloc_flex(*new_fn, name, ent_name->len + 1); + if (!new_fn) + return -ENOMEM; + new_fn->hash = hash; + new_fn->minor_hash = minor_hash; + new_fn->inode = le32_to_cpu(dirent->inode); + new_fn->name_len = ent_name->len; + new_fn->file_type = dirent->file_type; + memcpy(new_fn->name, ent_name->name, ent_name->len); + + while (*p) { + parent = *p; + fname = rb_entry(parent, struct fname, rb_hash); + + /* + * If the hash and minor hash match up, then we put + * them on a linked list. This rarely happens... + */ + if ((new_fn->hash == fname->hash) && + (new_fn->minor_hash == fname->minor_hash)) { + new_fn->next = fname->next; + fname->next = new_fn; + return 0; + } + + if (new_fn->hash < fname->hash) + p = &(*p)->rb_left; + else if (new_fn->hash > fname->hash) + p = &(*p)->rb_right; + else if (new_fn->minor_hash < fname->minor_hash) + p = &(*p)->rb_left; + else /* if (new_fn->minor_hash > fname->minor_hash) */ + p = &(*p)->rb_right; + } + + rb_link_node(&new_fn->rb_hash, parent, p); + rb_insert_color(&new_fn->rb_hash, &info->root); + return 0; +} + + + +/* + * This is a helper function for ext4_dx_readdir. It calls filldir + * for all entries on the fname linked list. (Normally there is only + * one entry on the linked list, unless there are 62 bit hash collisions.) + */ +static int call_filldir(struct file *file, struct dir_context *ctx, + struct fname *fname) +{ + struct dir_private_info *info = file->private_data; + struct inode *inode = file_inode(file); + struct super_block *sb = inode->i_sb; + + if (!fname) { + ext4_msg(sb, KERN_ERR, "%s:%d: inode #%llu: comm %s: " + "called with null fname?!?", __func__, __LINE__, + inode->i_ino, current->comm); + return 0; + } + ctx->pos = hash2pos(file, fname->hash, fname->minor_hash); + while (fname) { + if (!dir_emit(ctx, fname->name, + fname->name_len, + fname->inode, + get_dtype(sb, fname->file_type))) { + info->extra_fname = fname; + return 1; + } + fname = fname->next; + } + return 0; +} + +static int ext4_dx_readdir(struct file *file, struct dir_context *ctx) +{ + struct dir_private_info *info = file->private_data; + struct inode *inode = file_inode(file); + struct fname *fname; + int ret = 0; + + ext4_htree_init_dir_info(file, ctx->pos); + + if (ctx->pos == ext4_get_htree_eof(file)) + return 0; /* EOF */ + + /* Some one has messed with f_pos; reset the world */ + if (info->last_pos != ctx->pos) { + free_rb_tree_fname(&info->root); + info->curr_node = NULL; + info->extra_fname = NULL; + info->curr_hash = pos2maj_hash(file, ctx->pos); + info->curr_minor_hash = pos2min_hash(file, ctx->pos); + } + + /* + * If there are any leftover names on the hash collision + * chain, return them first. + */ + if (info->extra_fname) { + if (call_filldir(file, ctx, info->extra_fname)) + goto finished; + info->extra_fname = NULL; + goto next_node; + } else if (!info->curr_node) + info->curr_node = rb_first(&info->root); + + while (1) { + /* + * Fill the rbtree if we have no more entries, + * or the inode has changed since we last read in the + * cached entries. + */ + if ((!info->curr_node) || + !inode_eq_iversion(inode, info->cookie)) { + info->curr_node = NULL; + free_rb_tree_fname(&info->root); + info->cookie = inode_query_iversion(inode); + ret = ext4_htree_fill_tree(file, info->curr_hash, + info->curr_minor_hash, + &info->next_hash); + if (ret < 0) + goto finished; + if (ret == 0) { + ctx->pos = ext4_get_htree_eof(file); + break; + } + info->curr_node = rb_first(&info->root); + } + + fname = rb_entry(info->curr_node, struct fname, rb_hash); + info->curr_hash = fname->hash; + info->curr_minor_hash = fname->minor_hash; + if (call_filldir(file, ctx, fname)) + break; + next_node: + info->curr_node = rb_next(info->curr_node); + if (info->curr_node) { + fname = rb_entry(info->curr_node, struct fname, + rb_hash); + info->curr_hash = fname->hash; + info->curr_minor_hash = fname->minor_hash; + } else { + if (info->next_hash == ~0) { + ctx->pos = ext4_get_htree_eof(file); + break; + } + info->curr_hash = info->next_hash; + info->curr_minor_hash = 0; + } + } +finished: + info->last_pos = ctx->pos; + return ret < 0 ? ret : 0; +} + +static int ext4_release_dir(struct inode *inode, struct file *filp) +{ + if (filp->private_data) + ext4_htree_free_dir_info(filp->private_data); + + return 0; +} + +int ext4_check_all_de(struct inode *dir, struct buffer_head *bh, void *buf, + int buf_size) +{ + struct ext4_dir_entry_2 *de; + int rlen; + unsigned int offset = 0; + char *top; + + de = buf; + top = buf + buf_size; + while ((char *) de < top) { + if (ext4_check_dir_entry(dir, NULL, de, bh, + buf, buf_size, offset)) + return -EFSCORRUPTED; + rlen = ext4_rec_len_from_disk(de->rec_len, buf_size); + de = (struct ext4_dir_entry_2 *)((char *)de + rlen); + offset += rlen; + } + if ((char *) de > top) + return -EFSCORRUPTED; + + return 0; +} + +static int ext4_dir_open(struct inode *inode, struct file *file) +{ + struct dir_private_info *info; + + info = kzalloc_obj(*info); + if (!info) + return -ENOMEM; + file->private_data = info; + return 0; +} + +const struct file_operations ext4_dir_operations = { + .open = ext4_dir_open, + .llseek = ext4_dir_llseek, + .read = generic_read_dir, + .iterate_shared = ext4_readdir, + .unlocked_ioctl = ext4_ioctl, +#ifdef CONFIG_COMPAT + .compat_ioctl = ext4_compat_ioctl, +#endif + .fsync = ext4_sync_file, + .release = ext4_release_dir, + .setlease = generic_setlease, +}; -- cgit v1.3.1