Date: Fri, 27 Jun 1997 12:10:47 -0700 (PDT) From: Bill Paul <wpaul@FreeBSD.ORG> To: cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG, cvs-sys@FreeBSD.ORG Subject: cvs commit: src/sys/nfs nfs_vfsops.c Message-ID: <199706271910.MAA10921@freefall.freebsd.org>
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wpaul 1997/06/27 12:10:47 PDT
Modified files:
sys/nfs nfs_vfsops.c
Log:
Fix a condition where nfs_statfs() can precipitate a panic. There is
code that says this:
nfsm_request(vp, NFSPROC_FSSTAT, p, cred);
if (v3)
nfsm_postop_attr(vp, retattr);
if (!error)
nfsm_dissect(sfp, struct nfs_statfs *, NFSX_STATFS(v3));
The problem here is that if error != 0, nfsm_dissect() will not be
called, which leaves sfp == NULL. But nfs_statfs() does not bail out
at this point: it continues processing until it tries to dereference
sfp, which causes a panic. I was able to generate this crash under
the following conditions:
1) Set up a machine as an NFS server and NFS client, with amd running
(using NIS maps). /usr/local is exported, though any exported fs
can can be used to trigger the bug.
2) Log in as normal user, with home directory mounted from a SunOS 4.1.3
NFS server via amd (along with a few other NFS filesystems from same
machine).
3) Su to root and type the following:
# mount localhost:/usr/local /mnt
# df
To fix the panic, I changed the code to read:
if (!error) {
nfsm_dissect(sfp, struct nfs_statfs *, NFSX_STATFS(v3));
} else
goto nfsmout;
This is a bit kludgy in that nfsmout is a label defined by the nfsm_subs.h
macros, but these macros are themselves more than a little kludgy. This
stops the machine from crashing, but does not fix the overall bug: 'error'
somehow becomes 5 (EIO) when a statfs() is performed on the locally mounted
NFS filesystem. This seems to only happen the first time the filesystem
is accesed: on subsequent accesses, it seems to work fine again.
Now, I know there's no practical use in mounting a local filesystem
via NFS, but doing it shouldn't cause the system to melt down.
Revision Changes Path
1.44 +5 -2 src/sys/nfs/nfs_vfsops.c
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