4.14-stable review patch. If anyone has any objections, please let me know.
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From: Eddie.Horng eddie.horng@mediatek.com
commit 355139a8dba446cc11a424cddbf7afebc3041ba1 upstream.
The code in cap_inode_getsecurity(), introduced by commit 8db6c34f1dbc ("Introduce v3 namespaced file capabilities"), should use d_find_any_alias() instead of d_find_alias() do handle unhashed dentry correctly. This is needed, for example, if execveat() is called with an open but unlinked overlayfs file, because overlayfs unhashes dentry on unlink. This is a regression of real life application, first reported at https://www.spinics.net/lists/linux-unionfs/msg05363.html
Below reproducer and setup can reproduce the case. const char* exec="echo"; const char *newargv[] = { "echo", "hello", NULL}; const char *newenviron[] = { NULL }; int fd, err;
fd = open(exec, O_PATH); unlink(exec); err = syscall(322/*SYS_execveat*/, fd, "", newargv, newenviron, AT_EMPTY_PATH); if(err<0) fprintf(stderr, "execveat: %s\n", strerror(errno));
gcc compile into ~/test/a.out mount -t overlay -orw,lowerdir=/mnt/l,upperdir=/mnt/u,workdir=/mnt/w none /mnt/m cd /mnt/m cp /bin/echo . ~/test/a.out
Expected result: hello Actually result: execveat: Invalid argument dmesg: Invalid argument reading file caps for /dev/fd/3
The 2nd reproducer and setup emulates similar case but for regular filesystem: const char* exec="echo"; int fd, err; char buf[256];
fd = open(exec, O_RDONLY); unlink(exec); err = fgetxattr(fd, "security.capability", buf, 256); if(err<0) fprintf(stderr, "fgetxattr: %s\n", strerror(errno));
gcc compile into ~/test_fgetxattr
cd /tmp cp /bin/echo . ~/test_fgetxattr
Result: fgetxattr: Invalid argument
On regular filesystem, for example, ext4 read xattr from disk and return to execveat(), will not trigger this issue, however, the overlay attr handler pass real dentry to vfs_getxattr() will. This reproducer calls fgetxattr() with an unlinked fd, involkes vfs_getxattr() then reproduced the case that d_find_alias() in cap_inode_getsecurity() can't find the unlinked dentry.
Suggested-by: Amir Goldstein amir73il@gmail.com Acked-by: Amir Goldstein amir73il@gmail.com Acked-by: Serge E. Hallyn serge@hallyn.com Fixes: 8db6c34f1dbc ("Introduce v3 namespaced file capabilities") Cc: stable@vger.kernel.org # v4.14 Signed-off-by: Eddie Horng eddie.horng@mediatek.com Signed-off-by: Eric W. Biederman ebiederm@xmission.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- security/commoncap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/security/commoncap.c +++ b/security/commoncap.c @@ -388,7 +388,7 @@ int cap_inode_getsecurity(struct inode * if (strcmp(name, "capability") != 0) return -EOPNOTSUPP;
- dentry = d_find_alias(inode); + dentry = d_find_any_alias(inode); if (!dentry) return -EINVAL;