This is a note to let you know that I've just added the patch titled
afs: Fix use-after-free due to get/remove race in volume tree
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
afs-fix-use-after-free-due-to-get-remove-race-in-vol.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 6eccd848c86ce37dbe0372c02cb0ba6fc36cd6cd
Author: David Howells <dhowells@xxxxxxxxxx>
Date: Thu Dec 21 13:57:31 2023 +0000
afs: Fix use-after-free due to get/remove race in volume tree
[ Upstream commit 9a6b294ab496650e9f270123730df37030911b55 ]
When an afs_volume struct is put, its refcount is reduced to 0 before
the cell->volume_lock is taken and the volume removed from the
cell->volumes tree.
Unfortunately, this means that the lookup code can race and see a volume
with a zero ref in the tree, resulting in a use-after-free:
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 3 PID: 130782 at lib/refcount.c:25 refcount_warn_saturate+0x7a/0xda
...
RIP: 0010:refcount_warn_saturate+0x7a/0xda
...
Call Trace:
afs_get_volume+0x3d/0x55
afs_create_volume+0x126/0x1de
afs_validate_fc+0xfe/0x130
afs_get_tree+0x20/0x2e5
vfs_get_tree+0x1d/0xc9
do_new_mount+0x13b/0x22e
do_mount+0x5d/0x8a
__do_sys_mount+0x100/0x12a
do_syscall_64+0x3a/0x94
entry_SYSCALL_64_after_hwframe+0x62/0x6a
Fix this by:
(1) When putting, use a flag to indicate if the volume has been removed
from the tree and skip the rb_erase if it has.
(2) When looking up, use a conditional ref increment and if it fails
because the refcount is 0, replace the node in the tree and set the
removal flag.
Fixes: 20325960f875 ("afs: Reorganise volume and server trees to be rooted on the cell")
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Reviewed-by: Jeffrey Altman <jaltman@xxxxxxxxxxxx>
cc: Marc Dionne <marc.dionne@xxxxxxxxxxxx>
cc: linux-afs@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index b29e9c206f782..0c03877cdaf7e 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -589,6 +589,7 @@ struct afs_volume {
#define AFS_VOLUME_OFFLINE 4 /* - T if volume offline notice given */
#define AFS_VOLUME_BUSY 5 /* - T if volume busy notice given */
#define AFS_VOLUME_MAYBE_NO_IBULK 6 /* - T if some servers don't have InlineBulkStatus */
+#define AFS_VOLUME_RM_TREE 7 /* - Set if volume removed from cell->volumes */
#ifdef CONFIG_AFS_FSCACHE
struct fscache_cookie *cache; /* caching cookie */
#endif
@@ -1507,6 +1508,7 @@ extern struct afs_vlserver_list *afs_extract_vlserver_list(struct afs_cell *,
extern struct afs_volume *afs_create_volume(struct afs_fs_context *);
extern void afs_activate_volume(struct afs_volume *);
extern void afs_deactivate_volume(struct afs_volume *);
+bool afs_try_get_volume(struct afs_volume *volume, enum afs_volume_trace reason);
extern struct afs_volume *afs_get_volume(struct afs_volume *, enum afs_volume_trace);
extern void afs_put_volume(struct afs_net *, struct afs_volume *, enum afs_volume_trace);
extern int afs_check_volume_status(struct afs_volume *, struct afs_operation *);
diff --git a/fs/afs/volume.c b/fs/afs/volume.c
index 32941bffa2ec1..137a970c19fb3 100644
--- a/fs/afs/volume.c
+++ b/fs/afs/volume.c
@@ -33,8 +33,13 @@ static struct afs_volume *afs_insert_volume_into_cell(struct afs_cell *cell,
} else if (p->vid > volume->vid) {
pp = &(*pp)->rb_right;
} else {
- volume = afs_get_volume(p, afs_volume_trace_get_cell_insert);
- goto found;
+ if (afs_try_get_volume(p, afs_volume_trace_get_cell_insert)) {
+ volume = p;
+ goto found;
+ }
+
+ set_bit(AFS_VOLUME_RM_TREE, &volume->flags);
+ rb_replace_node_rcu(&p->cell_node, &volume->cell_node, &cell->volumes);
}
}
@@ -57,7 +62,8 @@ static void afs_remove_volume_from_cell(struct afs_volume *volume)
afs_volume_trace_remove);
write_seqlock(&cell->volume_lock);
hlist_del_rcu(&volume->proc_link);
- rb_erase(&volume->cell_node, &cell->volumes);
+ if (!test_and_set_bit(AFS_VOLUME_RM_TREE, &volume->flags))
+ rb_erase(&volume->cell_node, &cell->volumes);
write_sequnlock(&cell->volume_lock);
}
}
@@ -236,6 +242,20 @@ static void afs_destroy_volume(struct afs_net *net, struct afs_volume *volume)
_leave(" [destroyed]");
}
+/*
+ * Try to get a reference on a volume record.
+ */
+bool afs_try_get_volume(struct afs_volume *volume, enum afs_volume_trace reason)
+{
+ int r;
+
+ if (__refcount_inc_not_zero(&volume->ref, &r)) {
+ trace_afs_volume(volume->vid, r + 1, reason);
+ return true;
+ }
+ return false;
+}
+
/*
* Get a reference on a volume record.
*/
