Messages in this thread |  | | From | Schspa Shi <> | Subject | Re: [PATCH v3] 9p/fd: set req refcount to zero to avoid uninitialized usage | Date | Sun, 04 Dec 2022 22:35:41 +0800 |
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asmadeus@codewreck.org writes:
> Schspa Shi wrote on Thu, Dec 01, 2022 at 11:33:10AM +0800: >> When the new request allocated, the refcount will be zero if it is resued >> one. But if the request is newly allocated from slab, it is not fully >> initialized before add it 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 initize the refcount to zero before add to idr. > > (fixed initialize typo here) > >> Reported-by: syzbot+8f1060e2aaf8ca55220b@syzkaller.appspotmail.com >> Signed-off-by: Schspa Shi <schspa@gmail.com> >> >> -- >> >> Changelog: >> v1 -> v2: >> - Set refcount to fix the problem. >> v2 -> v3: >> - Comment messages improve as asmadeus suggested. > > Just a note: when applying a patch with git am, this goes into the > commit message -- please include the changelog below the git's three > dashes instead (anything between the three dashes and the 'diff --git' > below:
Thanks for the reminder, I will pay attention to this next time.
>> --- >> net/9p/client.c | 5 +++++ >> 1 file changed, 5 insertions(+) >> >> diff --git a/net/9p/client.c b/net/9p/client.c > > > Christian Schoenebeck wrote on Fri, Dec 02, 2022 at 12:48:39PM +0100: >> > + /* refcount needs to be set to 0 before inserting into the idr >> > + * so p9_tag_lookup does not accept a request that is not fully >> > + * initialized. refcount_set to 2 below will mark request live. >> > + */ >> > + refcount_set(&req->refcount, 0); >> >> I would s/live/ready for being used/, but comment should be clear enough >> anyway. > > I blame golfing to fit into three lines, sorry! > Since it was my suggestion, I've taken the liberty to change 'live' to > 'ready' as an half step; I think it's clearer than live and probably > understandable enough. > > I've pushed this to my next branch and will submit to Linus for the > merge window in a couple of weeks, no point in rushing this to stable > unless it gets snatched through the net tree first...
Thanks.
-- BRs Schspa Shi
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