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SubjectRe: [PATCH] fs/fcntl: restore checking against COMPAT_LOFF_T_MAX for F_GETLK64
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On Tue, 2017-11-14 at 04:30 +0300, Vitaly Lipatov wrote:
> for fcntl64 with F_GETLK64 we need use checking against COMPAT_LOFF_T_MAX.
>
> Fixes: 94073ad77fff2 "fs/locks: don't mess with the address limit in compat_fcntl64"
>
> Signed-off-by: Vitaly Lipatov <lav@etersoft.ru>
> ---
> fs/fcntl.c | 21 ++++++++++++++++++++-
> 1 file changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/fs/fcntl.c b/fs/fcntl.c
> index 30f47d0..fa17f67 100644
> --- a/fs/fcntl.c
> +++ b/fs/fcntl.c
> @@ -604,6 +604,25 @@ static int fixup_compat_flock(struct flock *flock)
> return 0;
> }
>
> +/*
> + * GETLK64 was successful and we need to return the data, but it needs to fit in
> + * the compat structure.
> + * l_start shouldn't be too big, unless the original start + end is greater than
> + * COMPAT_LOFF_T_MAX, in which case the app was asking for trouble, so we return
> + * -EOVERFLOW in that case. l_len could be too big, in which case we just
> + * truncate it, and only allow the app to see that part of the conflicting lock
> + * that might make sense to it anyway
> + */
> +
> +static int fixup_compat_l_flock(struct flock *flock)
> +{
> + if (flock->l_start > COMPAT_LOFF_T_MAX)
> + return -EOVERFLOW;
> + if (flock->l_len > COMPAT_LOFF_T_MAX)
> + flock->l_len = COMPAT_LOFF_T_MAX;
> + return 0;
> +}
> +

(cc'ing Christoph since he wrote the original patch)

This patch looks correct to me, but could we rename it to
fixup_compat_flock64 to match the other functions here?

Also, I think this should probably go to stable -- any objections?

> COMPAT_SYSCALL_DEFINE3(fcntl64, unsigned int, fd, unsigned int, cmd,
> compat_ulong_t, arg)
> {
> @@ -644,7 +663,7 @@ COMPAT_SYSCALL_DEFINE3(fcntl64, unsigned int, fd, unsigned int, cmd,
> err = fcntl_getlk(f.file, convert_fcntl_cmd(cmd), &flock);
> if (err)
> break;
> - err = fixup_compat_flock(&flock);
> + err = fixup_compat_l_flock(&flock);
> if (err)
> return err;
> err = put_compat_flock64(&flock, compat_ptr(arg));


--
Jeff Layton <jlayton@kernel.org>

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