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.
Fixes: bd64e57586d3 ("ovl: During copy up, first copy up metadata and then data") Cc: stable@vger.kernel.org # v4.19+ Reported-by: Giuseppe Scrivano gscrivan@redhat.com Signed-off-by: Vivek Goyal vgoyal@redhat.com --- fs/overlayfs/copy_up.c | 31 ++++++++++++++++++------------- 1 file changed, 18 insertions(+), 13 deletions(-)
Index: rhvgoyal-linux/fs/overlayfs/copy_up.c =================================================================== --- rhvgoyal-linux.orig/fs/overlayfs/copy_up.c 2019-01-10 17:25:25.594461223 -0500 +++ rhvgoyal-linux/fs/overlayfs/copy_up.c 2019-01-11 10:47:33.657461223 -0500 @@ -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,