linux-kernel - [PATCHv2] fs/9p: avoid debug OOPS when reading a long symlink

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Message-ID: <87mx1ok8xa.fsf_-_@rho.meyering.net>
Date:	Tue, 21 Aug 2012 09:20:49 +0200
From:	Jim Meyering <jim@...ering.net>
To:	linux-kernel@...r.kernel.org
Cc:	Eric Van Hensbergen <ericvh@...il.com>,
	Ron Minnich <rminnich@...dia.gov>,
	Latchesar Ionkov <lucho@...kov.net>,
	v9fs-developer@...ts.sourceforge.net
Subject: [PATCHv2] fs/9p: avoid debug OOPS when reading a long symlink


Reading a symlink longer than the given buffer, a p9_debug use would
try to print the link name (not NUL-terminated) using a %s format.
Use %.*s instead, and replace the strncpy+strnlen with functionally
equivalent strlen+memcpy.

Signed-off-by: Jim Meyering <meyering@...hat.com>
---
V1 provoked a warning due to strlen/buflen type differences (size_t/int)
and the "min" macro's type equality requirement.  This adds a cast to
avoid that warning:

-	retval = min(strlen(st->extension)+1, buflen);
+	retval = min(strlen(st->extension)+1, (size_t)buflen);

 fs/9p/vfs_inode.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
index cbf9dbb..890bed5 100644
--- a/fs/9p/vfs_inode.c
+++ b/fs/9p/vfs_inode.c
@@ -1276,12 +1276,12 @@ static int v9fs_readlink(struct dentry *dentry, char *buffer, int buflen)
 	}

 	/* copy extension buffer into buffer */
-	strncpy(buffer, st->extension, buflen);
+	retval = min(strlen(st->extension)+1, (size_t)buflen);
+	memcpy(buffer, st->extension, retval);

-	p9_debug(P9_DEBUG_VFS, "%s -> %s (%s)\n",
-		 dentry->d_name.name, st->extension, buffer);
+	p9_debug(P9_DEBUG_VFS, "%s -> %s (%.*s)\n",
+		 dentry->d_name.name, st->extension, buflen, buffer);

-	retval = strnlen(buffer, buflen);
 done:
 	p9stat_free(st);
 	kfree(st);
--
1.7.12
--
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