ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 237 insertions, 0 deletions

diff --git a/lib/ts_bm.c b/lib/ts_bm.c
new file mode 100644
index 000000000..676105e84
--- /dev/null
+++ b/lib/ts_bm.c
@@ -0,0 +1,237 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * lib/ts_bm.c		Boyer-Moore text search implementation
+ *
+ * Authors:	Pablo Neira Ayuso <pablo@eurodev.net>
+ *
+ * ==========================================================================
+ * 
+ *   Implements Boyer-Moore string matching algorithm:
+ *
+ *   [1] A Fast String Searching Algorithm, R.S. Boyer and Moore.
+ *       Communications of the Association for Computing Machinery, 
+ *       20(10), 1977, pp. 762-772.
+ *       https://www.cs.utexas.edu/users/moore/publications/fstrpos.pdf
+ *
+ *   [2] Handbook of Exact String Matching Algorithms, Thierry Lecroq, 2004
+ *       http://www-igm.univ-mlv.fr/~lecroq/string/string.pdf
+ *
+ *   Note: Since Boyer-Moore (BM) performs searches for matchings from right 
+ *   to left, it's still possible that a matching could be spread over 
+ *   multiple blocks, in that case this algorithm won't find any coincidence.
+ *   
+ *   If you're willing to ensure that such thing won't ever happen, use the
+ *   Knuth-Pratt-Morris (KMP) implementation instead. In conclusion, choose 
+ *   the proper string search algorithm depending on your setting. 
+ *
+ *   Say you're using the textsearch infrastructure for filtering, NIDS or 
+ *   any similar security focused purpose, then go KMP. Otherwise, if you 
+ *   really care about performance, say you're classifying packets to apply
+ *   Quality of Service (QoS) policies, and you don't mind about possible
+ *   matchings spread over multiple fragments, then go BM.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/string.h>
+#include <linux/ctype.h>
+#include <linux/textsearch.h>
+
+/* Alphabet size, use ASCII */
+#define ASIZE 256
+
+#if 0
+#define DEBUGP printk
+#else
+#define DEBUGP(args, format...)
+#endif
+
+struct ts_bm
+{
+	u8 *		pattern;
+	unsigned int	patlen;
+	unsigned int 	bad_shift[ASIZE];
+	unsigned int	good_shift[];
+};
+
+static unsigned int matchpat(const u8 *pattern, unsigned int patlen,
+			     const u8 *text, bool icase)
+{
+	unsigned int i;
+
+	for (i = 0; i < patlen; i++) {
+		u8 t = *(text-i);
+
+		if (icase)
+			t = toupper(t);
+
+		if (t != *(pattern-i))
+			break;
+	}
+
+	return i;
+}
+
+static unsigned int bm_find(struct ts_config *conf, struct ts_state *state)
+{
+	struct ts_bm *bm = ts_config_priv(conf);
+	unsigned int i, text_len, consumed = state->offset;
+	const u8 *text;
+	int bs;
+	const u8 icase = conf->flags & TS_IGNORECASE;
+
+	for (;;) {
+		int shift = bm->patlen - 1;
+
+		text_len = conf->get_next_block(consumed, &text, conf, state);
+
+		if (unlikely(text_len == 0))
+			break;
+
+		while (shift < text_len) {
+			DEBUGP("Searching in position %d (%c)\n",
+			       shift, text[shift]);
+
+			i = matchpat(&bm->pattern[bm->patlen-1], bm->patlen,
+				     &text[shift], icase);
+			if (i == bm->patlen) {
+				/* London calling... */
+				DEBUGP("found!\n");
+				return consumed + (shift-(bm->patlen-1));
+			}
+
+			bs = bm->bad_shift[text[shift-i]];
+
+			/* Now jumping to... */
+			shift = max_t(int, shift-i+bs, shift+bm->good_shift[i]);
+		}
+		consumed += text_len;
+	}
+
+	return UINT_MAX;
+}
+
+static int subpattern(u8 *pattern, int i, int j, int g)
+{
+	int x = i+g-1, y = j+g-1, ret = 0;
+
+	while(pattern[x--] == pattern[y--]) {
+		if (y < 0) {
+			ret = 1;
+			break;
+		}
+		if (--g == 0) {
+			ret = pattern[i-1] != pattern[j-1];
+			break;
+		}
+	}
+
+	return ret;
+}
+
+static void compute_prefix_tbl(struct ts_bm *bm, int flags)
+{
+	int i, j, g;
+
+	for (i = 0; i < ASIZE; i++)
+		bm->bad_shift[i] = bm->patlen;
+	for (i = 0; i < bm->patlen - 1; i++) {
+		bm->bad_shift[bm->pattern[i]] = bm->patlen - 1 - i;
+		if (flags & TS_IGNORECASE)
+			bm->bad_shift[tolower(bm->pattern[i])]
+			    = bm->patlen - 1 - i;
+	}
+
+	/* Compute the good shift array, used to match reocurrences 
+	 * of a subpattern */
+	bm->good_shift[0] = 1;
+	for (i = 1; i < bm->patlen; i++)
+		bm->good_shift[i] = bm->patlen;
+        for (i = bm->patlen-1, g = 1; i > 0; g++, i--) {
+		for (j = i-1; j >= 1-g ; j--)
+			if (subpattern(bm->pattern, i, j, g)) {
+				bm->good_shift[g] = bm->patlen-j-g;
+				break;
+			}
+	}
+}
+
+static struct ts_config *bm_init(const void *pattern, unsigned int len,
+				 gfp_t gfp_mask, int flags)
+{
+	struct ts_config *conf;
+	struct ts_bm *bm;
+	int i;
+	unsigned int prefix_tbl_len;
+	size_t priv_size;
+
+	/* Zero-length patterns would underflow bm_find()'s initial shift. */
+	if (unlikely(!len))
+		return ERR_PTR(-EINVAL);
+
+	/*
+	 * bm->pattern is stored immediately after the good_shift[] table.
+	 * Reject lengths that would wrap while sizing either region.
+	 */
+	if (unlikely(check_mul_overflow(len, sizeof(*bm->good_shift),
+					&prefix_tbl_len) ||
+		     check_add_overflow(sizeof(*bm), (size_t)len, &priv_size) ||
+		     check_add_overflow(priv_size, prefix_tbl_len, &priv_size)))
+		return ERR_PTR(-EINVAL);
+
+	conf = alloc_ts_config(priv_size, gfp_mask);
+	if (IS_ERR(conf))
+		return conf;
+
+	conf->flags = flags;
+	bm = ts_config_priv(conf);
+	bm->patlen = len;
+	bm->pattern = (u8 *) bm->good_shift + prefix_tbl_len;
+	if (flags & TS_IGNORECASE)
+		for (i = 0; i < len; i++)
+			bm->pattern[i] = toupper(((u8 *)pattern)[i]);
+	else
+		memcpy(bm->pattern, pattern, len);
+	compute_prefix_tbl(bm, flags);
+
+	return conf;
+}
+
+static void *bm_get_pattern(struct ts_config *conf)
+{
+	struct ts_bm *bm = ts_config_priv(conf);
+	return bm->pattern;
+}
+
+static unsigned int bm_get_pattern_len(struct ts_config *conf)
+{
+	struct ts_bm *bm = ts_config_priv(conf);
+	return bm->patlen;
+}
+
+static struct ts_ops bm_ops = {
+	.name		  = "bm",
+	.find		  = bm_find,
+	.init		  = bm_init,
+	.get_pattern	  = bm_get_pattern,
+	.get_pattern_len  = bm_get_pattern_len,
+	.owner		  = THIS_MODULE,
+	.list		  = LIST_HEAD_INIT(bm_ops.list)
+};
+
+static int __init init_bm(void)
+{
+	return textsearch_register(&bm_ops);
+}
+
+static void __exit exit_bm(void)
+{
+	textsearch_unregister(&bm_ops);
+}
+
+MODULE_DESCRIPTION("Boyer-Moore text search implementation");
+MODULE_LICENSE("GPL");
+
+module_init(init_bm);
+module_exit(exit_bm);