CVE-2022-50335
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2025-09-15

Last updated on: 2025-12-04

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: 9p: set req refcount to zero to avoid uninitialized usage When a new request is allocated, the refcount will be zero if it is reused, but if the request is newly allocated from slab, it is not fully initialized before being added to idr. If the p9_read_work got a response before the refcount initiated. It will use a uninitialized req, which will result in a bad request data struct. Here is the logs from syzbot. Corrupted memory at 0xffff88807eade00b [ 0xff 0x07 0x00 0x00 0x00 0x00 0x00 0x00 . . . . . . . . ] (in kfence-#110): p9_fcall_fini net/9p/client.c:248 [inline] p9_req_put net/9p/client.c:396 [inline] p9_req_put+0x208/0x250 net/9p/client.c:390 p9_client_walk+0x247/0x540 net/9p/client.c:1165 clone_fid fs/9p/fid.h:21 [inline] v9fs_fid_xattr_set+0xe4/0x2b0 fs/9p/xattr.c:118 v9fs_xattr_set fs/9p/xattr.c:100 [inline] v9fs_xattr_handler_set+0x6f/0x120 fs/9p/xattr.c:159 __vfs_setxattr+0x119/0x180 fs/xattr.c:182 __vfs_setxattr_noperm+0x129/0x5f0 fs/xattr.c:216 __vfs_setxattr_locked+0x1d3/0x260 fs/xattr.c:277 vfs_setxattr+0x143/0x340 fs/xattr.c:309 setxattr+0x146/0x160 fs/xattr.c:617 path_setxattr+0x197/0x1c0 fs/xattr.c:636 __do_sys_setxattr fs/xattr.c:652 [inline] __se_sys_setxattr fs/xattr.c:648 [inline] __ia32_sys_setxattr+0xc0/0x160 fs/xattr.c:648 do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline] __do_fast_syscall_32+0x65/0xf0 arch/x86/entry/common.c:178 do_fast_syscall_32+0x33/0x70 arch/x86/entry/common.c:203 entry_SYSENTER_compat_after_hwframe+0x70/0x82 Below is a similar scenario, the scenario in the syzbot log looks more complicated than this one, but this patch can fix it. T21124 p9_read_work ======================== second trans ================================= p9_client_walk p9_client_rpc p9_client_prepare_req p9_tag_alloc req = kmem_cache_alloc(p9_req_cache, GFP_NOFS); tag = idr_alloc << preempted >> req->tc.tag = tag; /* req->[refcount/tag] == uninitialized */ m->rreq = p9_tag_lookup(m->client, m->rc.tag); /* increments uninitalized refcount */ refcount_set(&req->refcount, 2); /* cb drops one ref */ p9_client_cb(req) /* reader thread drops its ref: request is incorrectly freed */ p9_req_put(req) /* use after free and ref underflow */ p9_req_put(req) To fix it, we can initialize the refcount to zero before add to idr.
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Meta Information
Published
2025-09-15
Last Modified
2025-12-04
Generated
2026-05-06
AI Q&A
2025-09-15
EPSS Evaluated
2026-05-05
NVD
CVE-2022-50335
Affected Vendors & Products
Showing 3 associated CPEs
Vendor Product Version / Range
linux linux_kernel From 4.19.57 (inc) to 5.15.86 (exc)
linux linux_kernel From 5.16 (inc) to 6.0.16 (exc)
linux linux_kernel From 6.1 (inc) to 6.1.2 (exc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-908 The product uses or accesses a resource that has not been initialized.
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?

This vulnerability in the Linux kernel's 9p client code occurs because a newly allocated request's reference count (refcount) is not properly initialized before being used. When a new request is allocated from the slab allocator, its refcount may be uninitialized. If a response is received before the refcount is set, the system uses this uninitialized request, leading to corrupted request data structures and potential use-after-free and reference count underflow issues. The fix involves initializing the refcount to zero before adding the request to the idr (ID radix tree) to prevent uninitialized usage.


How can this vulnerability impact me? :

This vulnerability can lead to memory corruption, use-after-free, and reference count underflow in the Linux kernel's 9p client subsystem. Such issues can cause system instability, crashes, or potentially allow attackers to execute arbitrary code or escalate privileges by exploiting the corrupted memory state.


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