Messages in this thread | | | Date | Fri, 2 Dec 2022 23:57:05 +0900 | From | asmadeus@codewrec ... | Subject | Re: [PATCH v3] 9p/fd: set req refcount to zero to avoid uninitialized usage |
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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: > --- > 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...
-- Dominique
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