From e873c74132f0c5f1452816cd9bb26208f0bba1e1 Mon Sep 17 00:00:00 2001 From: Shivank Garg Date: Sat, 22 Aug 2026 19:22:05 +0000 Subject: dmaengine: fix use-after-free in dma_chan_put() and dma_release_channel() When dma_device_put() drops the last reference on chan->device->ref, dma_device_release() runs and may free the dma_device along with its channels. dma_chan_put() then still reads chan->device->owner via dma_chan_to_owner() for the trailing module_put(). KASAN catches it: slab-use-after-free in dma_chan_put+0x3e6/0x4c0 Read of size 8 by task insmod/6319 Freed by task 6319: kfree+0x225/0x470 dma_chan_put+0x395/0x4c0 dmaengine_put+0xf8/0x160 Cache the module owner in dma_chan_put() before the put so the trailing module_put() does not need chan->device. Fixes: 8ad342a86359 ("dmaengine: Add reference counting to dma_device struct") Suggested-by: Sashiko Link: https://sashiko.dev/#/patchset/20260518-dmaengine-kref-fix-v1-1-4d6125048fb7@amd.com Reviewed-by: Frank Li Reviewed-by: Logan Gunthorpe Signed-off-by: Shivank Garg Link: https://patch.msgid.link/20260822-dmaengine-kref-fix-v5-3-d4a4ee47d927@amd.com Signed-off-by: Vinod Koul --- lib/lockref.c | 163 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 163 insertions(+) create mode 100644 lib/lockref.c (limited to 'lib/lockref.c') diff --git a/lib/lockref.c b/lib/lockref.c new file mode 100644 index 000000000..9b3dd688d --- /dev/null +++ b/lib/lockref.c @@ -0,0 +1,163 @@ +// SPDX-License-Identifier: GPL-2.0 +#include +#include + +#if USE_CMPXCHG_LOCKREF + +/* + * Note that the "cmpxchg()" reloads the "old" value for the + * failure case. + */ +#define CMPXCHG_LOOP(CODE, SUCCESS) do { \ + int retry = 100; \ + struct lockref old; \ + BUILD_BUG_ON(sizeof(old) != 8); \ + old.lock_count = READ_ONCE(lockref->lock_count); \ + while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) { \ + struct lockref new = old; \ + CODE \ + if (likely(try_cmpxchg64_relaxed(&lockref->lock_count, \ + &old.lock_count, \ + new.lock_count))) { \ + SUCCESS; \ + } \ + if (!--retry) \ + break; \ + } \ +} while (0) + +#else + +#define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0) + +#endif + +/** + * lockref_get - Increments reference count unconditionally + * @lockref: pointer to lockref structure + * + * This operation is only valid if you already hold a reference + * to the object, so you know the count cannot be zero. + */ +void lockref_get(struct lockref *lockref) +{ + CMPXCHG_LOOP( + new.count++; + , + return; + ); + + spin_lock(&lockref->lock); + lockref->count++; + spin_unlock(&lockref->lock); +} +EXPORT_SYMBOL(lockref_get); + +/** + * lockref_get_not_zero - Increments count unless the count is 0 or dead + * @lockref: pointer to lockref structure + * Return: 1 if count updated successfully or 0 if count was zero + */ +bool lockref_get_not_zero(struct lockref *lockref) +{ + bool retval = false; + + CMPXCHG_LOOP( + new.count++; + if (old.count <= 0) + return false; + , + return true; + ); + + spin_lock(&lockref->lock); + if (lockref->count > 0) { + lockref->count++; + retval = true; + } + spin_unlock(&lockref->lock); + return retval; +} +EXPORT_SYMBOL(lockref_get_not_zero); + +/** + * lockref_put_return - Decrement reference count if possible + * @lockref: pointer to lockref structure + * + * Decrement the reference count and return the new value. + * If the lockref was dead or locked, return -1. + */ +int lockref_put_return(struct lockref *lockref) +{ + CMPXCHG_LOOP( + new.count--; + if (old.count <= 0) + return -1; + , + return new.count; + ); + return -1; +} +EXPORT_SYMBOL(lockref_put_return); + +/** + * lockref_put_or_lock - decrements count unless count <= 1 before decrement + * @lockref: pointer to lockref structure + * Return: 1 if count updated successfully or 0 if count <= 1 and lock taken + */ +bool lockref_put_or_lock(struct lockref *lockref) +{ + CMPXCHG_LOOP( + new.count--; + if (old.count <= 1) + break; + , + return true; + ); + + spin_lock(&lockref->lock); + if (lockref->count <= 1) + return false; + lockref->count--; + spin_unlock(&lockref->lock); + return true; +} +EXPORT_SYMBOL(lockref_put_or_lock); + +/** + * lockref_mark_dead - mark lockref dead + * @lockref: pointer to lockref structure + */ +void lockref_mark_dead(struct lockref *lockref) +{ + assert_spin_locked(&lockref->lock); + lockref->count = __LOCKREF_DEAD_VAL; +} +EXPORT_SYMBOL(lockref_mark_dead); + +/** + * lockref_get_not_dead - Increments count unless the ref is dead + * @lockref: pointer to lockref structure + * Return: 1 if count updated successfully or 0 if lockref was dead + */ +bool lockref_get_not_dead(struct lockref *lockref) +{ + bool retval = false; + + CMPXCHG_LOOP( + new.count++; + if (old.count < 0) + return false; + , + return true; + ); + + spin_lock(&lockref->lock); + if (lockref->count >= 0) { + lockref->count++; + retval = true; + } + spin_unlock(&lockref->lock); + return retval; +} +EXPORT_SYMBOL(lockref_get_not_dead); -- cgit v1.3.1