CVE-2022-50335
Estado: ModificadaMedia (5.5)—
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.
Below is a similar scenario, the scenario in the syzbot log looks more complicated than this one, but this patch can fix it.
Leer descripción completaMostrar menos
To fix it, we can initialize the refcount to zero before add to idr.
Detalles técnicos trazas, registros y código del informe original
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
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)CVSS
- Versión: 3.1
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- Puntuación base: 5.5
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días: 0.38%
- Percentil entre todas las CVEs puntuadas: 30
- Fecha de la puntuación: 5/10/2026
EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).
Tecnologías afectadas (1)
CWE
- CWE-908
Referencias
JSON original (NVD)
Mostrar
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\n9p: set req refcount to zero to avoid uninitialized usage\n\nWhen a new request is allocated, the refcount will be zero if it is\nreused, but if the request is newly allocated from slab, it is not fully\ninitialized before being added to idr.\n\nIf the p9_read_work got a response before the refcount initiated. It will\nuse a uninitialized req, which will result in a bad request data struct.\n\nHere is the logs from syzbot.\n\nCorrupted memory at 0xffff88807eade00b [ 0xff 0x07 0x00 0x00 0x00 0x00\n0x00 0x00 . . . . . . . . ] (in kfence-#110):\n p9_fcall_fini net/9p/client.c:248 [inline]\n p9_req_put net/9p/client.c:396 [inline]\n p9_req_put+0x208/0x250 net/9p/client.c:390\n p9_client_walk+0x247/0x540 net/9p/client.c:1165\n clone_fid fs/9p/fid.h:21 [inline]\n v9fs_fid_xattr_set+0xe4/0x2b0 fs/9p/xattr.c:118\n v9fs_xattr_set fs/9p/xattr.c:100 [inline]\n v9fs_xattr_handler_set+0x6f/0x120 fs/9p/xattr.c:159\n __vfs_setxattr+0x119/0x180 fs/xattr.c:182\n __vfs_setxattr_noperm+0x129/0x5f0 fs/xattr.c:216\n __vfs_setxattr_locked+0x1d3/0x260 fs/xattr.c:277\n vfs_setxattr+0x143/0x340 fs/xattr.c:309\n setxattr+0x146/0x160 fs/xattr.c:617\n path_setxattr+0x197/0x1c0 fs/xattr.c:636\n __do_sys_setxattr fs/xattr.c:652 [inline]\n __se_sys_setxattr fs/xattr.c:648 [inline]\n __ia32_sys_setxattr+0xc0/0x160 fs/xattr.c:648\n do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline]\n __do_fast_syscall_32+0x65/0xf0 arch/x86/entry/common.c:178\n do_fast_syscall_32+0x33/0x70 arch/x86/entry/common.c:203\n entry_SYSENTER_compat_after_hwframe+0x70/0x82\n\nBelow is a similar scenario, the scenario in the syzbot log looks more\ncomplicated than this one, but this patch can fix it.\n\n T21124 p9_read_work\n======================== second trans =================================\np9_client_walk\n p9_client_rpc\n p9_client_prepare_req\n p9_tag_alloc\n req = kmem_cache_alloc(p9_req_cache, GFP_NOFS);\n tag = idr_alloc\n << preempted >>\n req->tc.tag = tag;\n /* req->[refcount/tag] == uninitialized */\n m->rreq = p9_tag_lookup(m->client, m->rc.tag);\n /* increments uninitalized refcount */\n\n refcount_set(&req->refcount, 2);\n /* cb drops one ref */\n p9_client_cb(req)\n /* reader thread drops its ref:\n request is incorrectly freed */\n p9_req_put(req)\n /* use after free and ref underflow */\n p9_req_put(req)\n\nTo fix it, we can initialize the refcount to zero before add to idr."
}
],
"lastModified": "2026-08-04T10:18:11.623",
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