netfs: break unbuffered write when netfs_alloc_subrequest() fails

Summary

In the Linux kernel, the following vulnerability has been resolved: netfs: break unbuffered write when netfs_alloc_subrequest() fails syzbot reported a null-ptr-deref below [1] following a fault injection in netfs_alloc_subrequest(). [0] When netfs_alloc_subrequest() fails, subreq is NULL. Later, netfs_prepare_write() tries to initialize members of subreq(e.g., source), the issue in [1] is triggered. Let's handle the error of netfs_prepare_write() properly. [0] FAULT_INJECTION: forcing a failure. name failslab, interval 1, probability 0, space 0, times 0 Call Trace: netfs_alloc_subrequest+0x116/0x3f0 netfs_prepare_write+0x76/0x7b0 netfs_unbuffered_write+0x75c/0x2020 netfs_unbuffered_write_iter_locked+0x7d6/0xa80 netfs_unbuffered_write_iter+0x442/0x720 v9fs_file_write_iter+0xbf/0x100 vfs_write+0x6ac/0x1050 [1] KASAN: null-ptr-deref in range [0x00000000000000a8-0x00000000000000af] RIP: 0010:netfs_prepare_write+0xbc/0x7b0 fs/netfs/write_issue.c:173 Call Trace: netfs_unbuffered_write+0x75c/0x2020 fs/netfs/direct_write.c:111 netfs_unbuffered_write_iter_locked+0x7d6/0xa80 fs/netfs/direct_write.c:290 netfs_unbuffered_write_iter+0x442/0x720 fs/netfs/direct_write.c:382 v9fs_file_write_iter+0xbf/0x100 fs/9p/vfs_file.c:409 new_sync_write fs/read_write.c:595 [inline]

Timeline

1. Sep 25, 2026, 10:36 AM UTCCVE published
2. Oct 19, 2026, 9:14 AM UTCRecord last updated

Affected versions

• Linux Linux

  From 288ace2f57c9d06dd2e42bd80d03747d879a4068 · fixed in cf6f93b8b06acf57de62dacbe71a3b99c68656a7; From 288ace2f57c9d06dd2e42bd80d03747d879a4068 · fixed in 19f246c795e940dc5f11cd5bc0cb1e81bc7b7090; From 288ace2f57c9d06dd2e42bd80d03747d879a4068 · fixed in 8fb45a934661419c04a44d4cfea1e0df7dcf2805

• Linux Linux

  6.10

• KernelLinux

  From 6.10.0 · fixed in 6.18.53; From 6.19.0 · fixed in 7.2.7

References 3