On Tue, Jun 05, 2018 at 02:49:20PM -0500, Eric Sandeen wrote: > From: Arnd Bergmann <arnd@xxxxxxxx> > > [sandeen: fix subject, avoid copy-out of uninit data in getlabel] > > gcc-8 reports two warnings for the newly added getlabel/setlabel code: > > 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)); > ^ > 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. > > 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> > Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx> Working around strncpy warnings with memcpy? I guess... Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> --D > --- > > diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c > index 82f7c83c1dad..596e176c19a6 100644 > --- a/fs/xfs/xfs_ioctl.c > +++ b/fs/xfs/xfs_ioctl.c > @@ -1828,13 +1828,13 @@ xfs_ioc_getlabel( > /* Paranoia */ > BUILD_BUG_ON(sizeof(sbp->sb_fname) > FSLABEL_MAX); > > + /* 1 larger than sb_fname, so this ensures a trailing NUL char */ > + memset(label, 0, sizeof(label)); > spin_lock(&mp->m_sb_lock); > - strncpy(label, sbp->sb_fname, sizeof(sbp->sb_fname)); > + strncpy(label, sbp->sb_fname, XFSLABEL_MAX); > 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))) > return -EFAULT; > return 0; > } > @@ -1870,7 +1870,7 @@ 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); > spin_unlock(&mp->m_sb_lock); > > /* > > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
