overlayfs: During copy up, first copy up data and then xattrs
Subsystems (2)
PATCH v3 1/1 overlayfs: During copy up, first copy up data and then xattrs
If a file with capability set (and hence security.capability xattr) is written kernel clears security.capability xattr. For overlay, during file copy up if xattrs are copied up first and then data is, copied up. This means data copy up will result in clearing of security.capability xattr file on lower has. And this can result into surprises. If
a lower file has CAP_SETUID, then it should not be cleared over copy up (if nothing was actually written to file).
This also creates problems with chown logic where it first copies up file and then tries to clear setuid bit. But by that time security.capability xattr is already gone (due to data copy up), and caller gets -ENODATA. This has been reported by Giuseppe here.
https://github.com/containers/libpod/issues/2015#issuecomment-447824842
Fix this by copying up data first and then metadta. This is a regression which has been introduced by my commit as part of metadata only copy up patches.
TODO: There will be some corner cases where a file is copied up metadata
only and later data copy up happens and that will clear security.capability xattr. Something needs to be done about that too.
--- fs/overlayfs/copy_up.c | 31 ++++++++++++++++++------------- 1 file changed, 18 insertions(+), 13 deletions(-)
fs/overlayfs/copy_up.c +18 -13
@@ -443,6 +443,24 @@ static int ovl_copy_up_inode(struct ovl_ {int err; +/* +* Copy up data first and then xattrs. Writing data after +* xattrs will remove security.capability xattr automatically. +*/ +if (S_ISREG (c->stat.mode) && !c->metacopy) { +struct path upperpath, datapath; + +ovl_path_upper (c->dentry, &upperpath); +if (WARN_ON (upperpath.dentry !=NULL )) +return -EIO ; + upperpath.dentry = temp; + +ovl_path_lowerdata (c->dentry, &datapath); + err =ovl_copy_up_data (&datapath, &upperpath, c->stat.size); +if (err) +return err; + } + err =ovl_copy_xattr (c->lowerpath.dentry, temp);if (err)return err;
@@ -459,19 +477,6 @@ static int ovl_copy_up_inode(struct ovl_if (err)return err; } - -if (S_ISREG (c->stat.mode) && !c->metacopy) { -struct path upperpath, datapath; - -ovl_path_upper (c->dentry, &upperpath); -BUG_ON (upperpath.dentry !=NULL ); - upperpath.dentry = temp; - -ovl_path_lowerdata (c->dentry, &datapath); - err =ovl_copy_up_data (&datapath, &upperpath, c->stat.size); -if (err) -return err; - }if (c->metacopy) { err = ovl_check_setxattr(c->dentry, temp, OVL_XATTR_METACOPY,
Quoted 20 lines · Vivek Goyal
If a file with capability set (and hence security.capability xattr) is written kernel clears security.capability xattr. For overlay, during file copy up if xattrs are copied up first and then data is, copied up. This means data copy up will result in clearing of security.capability xattr file on lower has. And this can result into surprises. If
a lower file hasCAP_SETUID, then it should not be cleared over copy up (if nothing was actually written to file).This also creates problems with chown logic where it first copies up file and then tries to clear setuid bit. But by that time security.capability xattr is already gone (due to data copy up), and caller gets
-ENODATA. This has been reported by Giuseppe here.https://github.com/containers/libpod/issues/2015#issuecomment-447824842
Fix this by copying up data first and then metadta. This is a regression which has been introduced by my commit as part of metadata only copy up patches.
Quoted 8 lines
TODO: There will be some corner cases where a file is copied up metadata
only and later data copy up happens and that will clear security.capability xattr. Something needs to be done about that too.Fixes bd64e57586d3 ("ovl: During copy up, first copy up metadata and then data")Cc <[email protected]> # v4.19+Reported-by Giuseppe Scrivano <[email protected]>Signed-off-by Vivek Goyal <[email protected]>
Thanks, applied.
Miklos