fsnotify: prevent mark additions during connector teardown
Impact
In the Linux kernel, the following vulnerability has been resolved:
Source excerpt · LinuxAffected packages
Affected products
Vendor version evidence. Product records are separate from automatic dependency matching.
Linux · Linux
Other versions: unaffected
| Version / range | Source status |
|---|---|
| 6b3f05d24d355f50f3d9814304650fcab0efb482 to before 952501bfc6e5e654ac4a17ec9d90c1ec614bd9f1 | affected |
| 6b3f05d24d355f50f3d9814304650fcab0efb482 to before 472589eacdf10b5f9bd10b333957ed5291b2544b | affected |
| 6b3f05d24d355f50f3d9814304650fcab0efb482 to before 36ebddca56b9d8993d6dc984fdecc748ee1f5e06 | affected |
Linux · Linux
Other versions: affected
| Version / range | Source status |
|---|---|
| 4.12 | affected |
| 0 to before 4.12 | unaffected |
| 6.18.59 through 6.18.* (inclusive) | unaffected |
| 7.2.13 through 7.2.* (inclusive) | unaffected |
| 7.3 through * (inclusive) | unaffected |
Original source description
In the Linux kernel, the following vulnerability has been resolved:
fsnotify: prevent mark additions during connector teardown
fsnotify_destroy_marks() keeps a reference to its current mark while it drops conn->lock to destroy the mark. This stabilizes the forward-walk cursor, but does not prevent a new mark from being inserted before it. For example, an inotify watch re-added after IN_IGNORED sorts before the old, detached mark for the same group. The walk can miss the replacement and then detach the entire connector from the object.
The replacement is still on its group's marks_list and, for inotify, in the watch IDR. The group mutex no longer protects the connector's object from disappearing. An unprivileged fdinfo read racing the final detach can consequently call igrab(NULL):
BUG: KASAN: null-ptr-deref in igrab+0x24/0x100 Write of size 4 at addr 0000000000000148 Call Trace: igrab+0x24/0x100 inotify_show_fdinfo+0x1dc/0x5e0 seq_show+0x397/0x690
Set a DESTROYING flag under conn->lock before starting the walk, and reject new marks on that connector with -ENOENT. The existing add-mark error paths undo the temporary group-list entry and the backend's watch allocation. Do not wait for teardown while holding the group mutex, which the destroyer needs. Once the old connector is detached, an add can install a fresh connector as before.
This closes the insertion race for all object types using the common connector teardown, without changing the mark reference or SRCU lifetime rules.