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SubjectRe: [PATCH v2] ext4: Prevent stack overrun in ext4_file_open when recording last known mountpoint
On Fri, Sep 16, 2011 at 11:40:05AM -0700, Darrick J. Wong wrote:
> In ext4_file_open, the filesystem records the mountpoint of the first file that
> is opened after mounting the filesystem. It does this by allocating a 64-byte
> stack buffer, calling d_path() to grab the mount point through which this file
> was accessed, and then memcpy()ing 64 bytes into the superblock's
> s_last_mounted field, starting from the return value of d_path(), which is
> stored as "cp". However, if cp > buf (which it frequently is since path
> components are prepended starting at the end of buf) then we can end up copying
> stack data into the superblock.
>
> Writing stack variables into the superblock doesn't sound like a great idea, so
> use strlcpy instead. Andi Kleen suggested using strlcpy instead of strncpy.

Ok, it's been a couple of weeks.... any thoughts, Ted?
--D
>
> Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
> ---
>
> fs/ext4/file.c | 4 ++--
> 1 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index e4095e9..9781099 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -181,8 +181,8 @@ static int ext4_file_open(struct inode * inode, struct file * filp)
> path.dentry = mnt->mnt_root;
> cp = d_path(&path, buf, sizeof(buf));
> if (!IS_ERR(cp)) {
> - memcpy(sbi->s_es->s_last_mounted, cp,
> - sizeof(sbi->s_es->s_last_mounted));
> + strlcpy(sbi->s_es->s_last_mounted, cp,
> + sizeof(sbi->s_es->s_last_mounted));
> ext4_mark_super_dirty(sb);
> }
> }
> --
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