CVE-2022-49810

In the Linux kernel, the following vulnerability has been resolved:

netfs: Fix missing xas_retry() calls in xarray iteration

netfslib has a number of places in which it performs iteration of an xarray whilst being under the RCU read lock. It should call xas_retry() as the first thing inside of the loop and do "continue" if it returns true in case the xarray walker passed out a special value indicating that the walk needs to be redone from the root[*].

Fix this by adding the missing retry checks.

[*] I wonder if this should be done inside xas_find(), xas_next_node() and suchlike, but I'm told that's not an simple change to effect.

This can cause an oops like that below. Note the faulting address - this is an internal value (|0x2) returned from xarray.

BUG: kernel NULL pointer dereference, address: 0000000000000402 ... RIP: 0010:netfs_rreq_unlock+0xef/0x380 [netfs] ... Call Trace: netfs_rreq_assess+0xa6/0x240 [netfs] netfs_readpage+0x173/0x3b0 [netfs] ? init_wait_var_entry+0x50/0x50 filemap_read_page+0x33/0xf0 filemap_get_pages+0x2f2/0x3f0 filemap_read+0xaa/0x320 ? do_filp_open+0xb2/0x150 ? rmqueue+0x3be/0xe10 ceph_read_iter+0x1fe/0x680 [ceph] ? new_sync_read+0x115/0x1a0 new_sync_read+0x115/0x1a0 vfs_read+0xf3/0x180 ksys_read+0x5f/0xe0 do_syscall_64+0x38/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae

Changes:

ver #2)

• Changed an unsigned int to a size_t to reduce the likelihood of an overflow as per Willy's suggestion.
• Added an additional patch to fix the maths.

A missing xas_retry() check in netfs could lead to NULL pointer dereference during xarray iteration under RCU. Exploiting this requires root privileges or a custom kernel module that triggers specific race conditions in netfs operations, which are not accessible to regular users.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.