From: Mingyu Wang <[email protected]>
Syzkaller fuzzer triggered a kernel panic via a WARNING in
drm_prime_destroy_file_private() due to a non-empty prime rb_tree.
The root cause is a complete lack of synchronization in the teardown
path. While the import path (drm_gem_prime_fd_to_handle) holds the
&file_priv->prime.lock during lookup and insertion, the deletion path
(drm_prime_remove_buf_handle) traverses and mutates both the 'handles'
and 'dmabufs' rb_trees without acquiring any mutex.
When multiple threads concurrently close GEM handles or interleave import
and close operations, the pointers and balance states of the rb_tree
nodes get corrupted. As a result, certain members are erased from one
tree but remain orphaned in the other. Upon process exit, the final
sanity check triggers the WARNING.
[ 448.919314][T19739] ------------[ cut here ]------------
[ 448.945387][T19739] WARNING: CPU: 0 PID: 19739 at
drivers/gpu/drm/drm_prime.c:223 drm_prime_destroy_file_private+0x43/0x60
...
[ 449.056535][T19739] Call Trace:
[ 449.056544][T19739] <TASK>
[ 449.056553][T19739] drm_file_free.part.0+0x805/0xcf0
[ 449.056652][T19739] drm_close_helper.isra.0+0x183/0x1f0
[ 449.056677][T19739] drm_release+0x1ab/0x360
[ 449.056719][T19739] __fput+0x402/0xb50
[ 449.056783][T19739] task_work_run+0x16b/0x260
[ 449.056883][T19739] exit_to_user_mode_loop+0xf9/0x130
[ 449.056931][T19739] do_syscall_64+0x424/0xfa0
[ 449.056977][T19739] entry_SYSCALL_64_after_hwframe+0x77/0x7f
[ 449.057268][T19739] </TASK>
[ 449.057295][T19739] Kernel panic - not syncing: kernel: panic_on_warn set
...
Fix this by acquiring the prime_fpriv->lock mutex around the rb_tree
lookup and erasure logic. To respect the locking rules and avoid potential
deadlocks with driver-specific memory cleanups, assign the target node to
a temporary pointer and defer the dma_buf_put() and kfree() operations
until after the mutex is safely dropped.
Fixes: ea2aa97ca37a ("drm/gem: Fix GEM handle release errors")
Cc: [email protected]
Signed-off-by: Mingyu Wang <[email protected]>
---
drivers/gpu/drm/drm_prime.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 9b44c78cd77f..26319c638e0f 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -190,6 +190,9 @@ void drm_prime_remove_buf_handle(struct
drm_prime_file_private *prime_fpriv,
uint32_t handle)
{
struct rb_node *rb;
+ struct drm_prime_member *found = NULL;
+
+ mutex_lock(&prime_fpriv->lock);
rb = prime_fpriv->handles.rb_node;
while (rb) {
@@ -200,8 +203,7 @@ void drm_prime_remove_buf_handle(struct
drm_prime_file_private *prime_fpriv,
rb_erase(&member->handle_rb, &prime_fpriv->handles);
rb_erase(&member->dmabuf_rb, &prime_fpriv->dmabufs);
- dma_buf_put(member->dma_buf);
- kfree(member);
+ found = member;
break;
} else if (member->handle < handle) {
rb = rb->rb_right;
@@ -209,6 +211,13 @@ void drm_prime_remove_buf_handle(struct
drm_prime_file_private *prime_fpriv,
rb = rb->rb_left;
}
}
+ mutex_unlock(&prime_fpriv->lock);
+
+ /* Defer resource release outside the mutex to prevent deadlocks */
+ if (found) {
+ dma_buf_put(found->dma_buf);
+ kfree(found);
+ }
}
void drm_prime_init_file_private(struct drm_prime_file_private *prime_fpriv)
--
2.34.1
