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Subject[PATCHv2] fs/9p: avoid debug OOPS when reading a long symlink
Date

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@redhat.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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