linux-kernel - [PATCH 3.16 113/233] staging/lustre/lov: remove set_fs() call from lov

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Date:   Sat, 09 Sep 2017 22:47:14 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Oleg Drokin" <green@...uxhacker.ru>,
        "Andreas Dilger" <andreas.dilger@...el.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "John L. Hammond" <john.hammond@...el.com>,
        "Li Wei" <wei.g.li@...el.com>
Subject: [PATCH 3.16 113/233] staging/lustre/lov: remove set_fs() call
 from lov_getstripe()

3.16.48-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Oleg Drokin <green@...uxhacker.ru>

commit 0a33252e060e97ed3fbdcec9517672f1e91aaef3 upstream.

lov_getstripe() calls set_fs(KERNEL_DS) so that it can handle a struct
lov_user_md pointer from user- or kernel-space.  This changes the
behavior of copy_from_user() on SPARC and may result in a misaligned
access exception which in turn oopses the kernel.  In fact the
relevant argument to lov_getstripe() is never called with a
kernel-space pointer and so changing the address limits is unnecessary
and so we remove the calls to save, set, and restore the address
limits.

Signed-off-by: John L. Hammond <john.hammond@...el.com>
Reviewed-on: http://review.whamcloud.com/6150
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3221
Reviewed-by: Andreas Dilger <andreas.dilger@...el.com>
Reviewed-by: Li Wei <wei.g.li@...el.com>
Signed-off-by: Oleg Drokin <green@...uxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/staging/lustre/lustre/lov/lov_pack.c | 9 ---------
 1 file changed, 9 deletions(-)

--- a/drivers/staging/lustre/lustre/lov/lov_pack.c
+++ b/drivers/staging/lustre/lustre/lov/lov_pack.c
@@ -592,18 +592,10 @@ int lov_getstripe(struct obd_export *exp
 	struct lov_mds_md *lmmk = NULL;
 	int rc, lmm_size;
 	int lum_size;
-	mm_segment_t seg;
 
 	if (!lsm)
 		return -ENODATA;
 
-	/*
-	 * "Switch to kernel segment" to allow copying from kernel space by
-	 * copy_{to,from}_user().
-	 */
-	seg = get_fs();
-	set_fs(KERNEL_DS);
-
 	/* we only need the header part from user space to get lmm_magic and
 	 * lmm_stripe_count, (the header part is common to v1 and v3) */
 	lum_size = sizeof(struct lov_user_md_v1);
@@ -672,6 +664,5 @@ int lov_getstripe(struct obd_export *exp
 
 	obd_free_diskmd(exp, &lmmk);
 out_set:
-	set_fs(seg);
 	return rc;
 }