Thanks, applying for 3.11.--b.
On Tue, Jul 23, 2013 at 02:21:35PM +1000, Harshula Jayasuriya wrote:
> The following call chain:
> ------------------------------------------------------------
> nfs4_get_vfs_file
> - nfsd_open
> - dentry_open
> - do_dentry_open
> - __get_file_write_access
> - get_write_access
> - return atomic_inc_unless_negative(&inode->i_writecount) ? 0 : -ETXTBSY;
> ------------------------------------------------------------
>
> can result in the following state:
> ------------------------------------------------------------
> struct nfs4_file {
> ...
> fi_fds = {0xffff880c1fa65c80, 0xffffffffffffffe6, 0x0},
> fi_access = {{
> counter = 0x1
> }, {
> counter = 0x0
> }},
> ...
> ------------------------------------------------------------
>
> 1) First time around, in nfs4_get_vfs_file() fp->fi_fds[O_WRONLY] is
> NULL, hence nfsd_open() is called where we get status set to an error
> and fp->fi_fds[O_WRONLY] to -ETXTBSY. Thus we do not reach
> nfs4_file_get_access() and fi_access[O_WRONLY] is not incremented.
>
> 2) Second time around, in nfs4_get_vfs_file() fp->fi_fds[O_WRONLY] is
> NOT NULL (-ETXTBSY), so nfsd_open() is NOT called, but
> nfs4_file_get_access() IS called and fi_access[O_WRONLY] is incremented.
> Thus we leave a landmine in the form of the nfs4_file data structure in
> an incorrect state.
>
> 3) Eventually, when __nfs4_file_put_access() is called it finds
> fi_access[O_WRONLY] being non-zero, it decrements it and calls
> nfs4_file_put_fd() which tries to fput -ETXTBSY.
> ------------------------------------------------------------
> ...
> [exception RIP: fput+0x9]
> RIP: ffffffff81177fa9 RSP: ffff88062e365c90 RFLAGS: 00010282
> RAX: ffff880c2b3d99cc RBX: ffff880c2b3d9978 RCX: 0000000000000002
> RDX: dead000000100101 RSI: 0000000000000001 RDI: ffffffffffffffe6
> RBP: ffff88062e365c90 R8: ffff88041fe797d8 R9: ffff88062e365d58
> R10: 0000000000000008 R11: 0000000000000000 R12: 0000000000000001
> R13: 0000000000000007 R14: 0000000000000000 R15: 0000000000000000
> ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
> #9 [ffff88062e365c98] __nfs4_file_put_access at ffffffffa0562334 [nfsd]
> #10 [ffff88062e365cc8] nfs4_file_put_access at ffffffffa05623ab [nfsd]
> #11 [ffff88062e365ce8] free_generic_stateid at ffffffffa056634d [nfsd]
> #12 [ffff88062e365d18] release_open_stateid at ffffffffa0566e4b [nfsd]
> #13 [ffff88062e365d38] nfsd4_close at ffffffffa0567401 [nfsd]
> #14 [ffff88062e365d88] nfsd4_proc_compound at ffffffffa0557f28 [nfsd]
> #15 [ffff88062e365dd8] nfsd_dispatch at ffffffffa054543e [nfsd]
> #16 [ffff88062e365e18] svc_process_common at ffffffffa04ba5a4 [sunrpc]
> #17 [ffff88062e365e98] svc_process at ffffffffa04babe0 [sunrpc]
> #18 [ffff88062e365eb8] nfsd at ffffffffa0545b62 [nfsd]
> #19 [ffff88062e365ee8] kthread at ffffffff81090886
> #20 [ffff88062e365f48] kernel_thread at ffffffff8100c14a
> ------------------------------------------------------------
>
> Signed-off-by: Harshula Jayasuriya <harshula@xxxxxxxxxx>
> ---
> fs/nfsd/vfs.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index 8ff6a00..c827acb 100644
> --- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -830,9 +830,10 @@ nfsd_open(struct svc_rqst *rqstp, struct svc_fh *fhp, umode_t type,
> flags = O_WRONLY|O_LARGEFILE;
> }
> *filp = dentry_open(&path, flags, current_cred());
> - if (IS_ERR(*filp))
> + if (IS_ERR(*filp)) {
> host_err = PTR_ERR(*filp);
> - else {
> + *filp = NULL;
> + } else {
> host_err = ima_file_check(*filp, may_flags);
>
> if (may_flags & NFSD_MAY_64BIT_COOKIE)
> --
> 1.8.1.4
>
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