On 5/25/18 10:14 AM, Arnd Bergmann wrote:
gcc-8 reports two warnings for the newly added getlabel/setlabel code:
Thanks for catching these.
The patch summary confuses me, what does "mark sb_fname as nonstring"
mean in the context of the actual patch?
I hate strings in C! ;)
fs/xfs/xfs_ioctl.c: In function 'xfs_ioc_getlabel':
fs/xfs/xfs_ioctl.c:1822:38: error: argument to 'sizeof' in 'strncpy' call is the same expression as the source; did you mean to use the size of the destination? [-Werror=sizeof-pointer-memaccess]
strncpy(label, sbp->sb_fname, sizeof(sbp->sb_fname)); ^
o_O hrpmh.
In function 'strncpy',
inlined from 'xfs_ioc_setlabel' at /git/arm-soc/fs/xfs/xfs_ioctl.c:1863:2,
inlined from 'xfs_file_ioctl' at /git/arm-soc/fs/xfs/xfs_ioctl.c:1918:10:
include/linux/string.h:254:9: error: '__builtin_strncpy' output may be truncated copying 12 bytes from a string of length 12 [-Werror=stringop-truncation]
return __builtin_strncpy(p, q, size);
In both cases, part of the problem is that one of the strncpy()
arguments is a fixed-length character array with zero-padding rather
than a zero-terminated string. In the first one case, we also get an
odd warning about sizeof-pointer-memaccess, which doesn't seem right
(the sizeof is for an array that happens to be the same as the second
strncpy argument).
To work around the bogus warning, I use a plain 'XFSLABEL_MAX' for
the strncpy() length when copying the label in getlabel. For setlabel(),
using memcpy() with the correct length that is already known avoids
the second warning and is slightly simpler.
In a related issue, it appears that we accidentally skip the trailing
\0 when copying a 12-character label back to user space in getlabel().
Using the correct sizeof() argument here copies the extra character.
Oops, you are correct. Sigh, I wonder why testing didn't see that.
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85602
Fixes: f7664b31975b ("xfs: implement online get/set fs label")
Cc: Eric Sandeen <sandeen@xxxxxxxxxx>
Cc: Martin Sebor <msebor@xxxxxxxxx>
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
fs/xfs/xfs_ioctl.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index 84fbf164cbc3..eb79f2bc4dcc 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -1819,12 +1819,12 @@ xfs_ioc_getlabel(
BUILD_BUG_ON(sizeof(sbp->sb_fname) > FSLABEL_MAX);
spin_lock(&mp->m_sb_lock);
- strncpy(label, sbp->sb_fname, sizeof(sbp->sb_fname));
+ strncpy(label, sbp->sb_fname, XFSLABEL_MAX);
ok
spin_unlock(&mp->m_sb_lock);
/* xfs on-disk label is 12 chars, be sure we send a null to user */
label[XFSLABEL_MAX] = '\0';
- if (copy_to_user(user_label, label, sizeof(sbp->sb_fname)))
+ if (copy_to_user(user_label, label, sizeof(label)))
ok. (odd how this is ok for copy_to_user but not for strncpy above) :)
return -EFAULT;
return 0;
}
@@ -1860,7 +1860,7 @@ xfs_ioc_setlabel(
spin_lock(&mp->m_sb_lock);
memset(sbp->sb_fname, 0, sizeof(sbp->sb_fname));
- strncpy(sbp->sb_fname, label, sizeof(sbp->sb_fname));
+ memcpy(sbp->sb_fname, label, len);
Hm but len = strnlen(label, XFSLABEL_MAX + 1);
which could be one longer than sbp->sb_fname, no?
spin_unlock(&mp->m_sb_lock);
/*
--
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