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afs: Fix use-after-free due to get/remove race in volume tree

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[ 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: 20325960f8 ("afs: Reorganise volume and server trees to be rooted on the cell")
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeffrey Altman <jaltman@auristor.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
David Howells 2023-12-21 13:57:31 +00:00 committed by Greg Kroah-Hartman
parent 17605162e2
commit 9b4c95a63e
2 changed files with 25 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
fs/afs/internal.h
View File

@ -585,6 +585,7 @@ 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_volume *cache; /* Caching cookie */
#endif
@ -1517,6 +1518,7 @@ extern struct afs_vlserver_list *afs_extract_vlserver_list(struct afs_cell *,
extern struct afs_volume *afs_create_volume(struct afs_fs_context *);
extern int 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 *);

26
fs/afs/volume.c
View File

@ -32,8 +32,13 @@ 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);
}
}
@ -56,7 +61,8 @@ 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);
}
}
@ -235,6 +241,20 @@ 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.
*/