libmount: check for linux/mount.h

Check that linux/mount.h is present before using features that rely on
it.

It is necessary to check for the presence of linux/mount.h explicitly.
Simply relying on the presence of several syscalls (e.g. SYS_move_mount,
SYS_open_tree) does not work reliably, at least not in a cross-compiling
environment.

The syscall definitions are provided by the C library. Meanwhile,
linux/mount.h is provided by the kernel. This opens the possibility for
discrepancies.

A problem arises if the C library (e.g. musl-1.2.3) defines all "mount
fd API" syscalls (and HAVE_MOUNTFD_API becomes true), but the kernel
headers are old enough to not provide linux/mount.h. The resulting error
looks as follows. This example is using an LLVM-13 cross-compiler from
x86_64 to aarch64 with musl-1.2.3 as the C library.

  CC       libmount/src/la-hooks.lo
In file included from libmount/src/hooks.c:30:
./include/mount-api-utils.h:11:10: fatal error: 'linux/mount.h' file not found
         ^~~~~~~~~~~~~~~
1 error generated.
make[4]: *** [Makefile:11185: libmount/src/la-hooks.lo] Error 1

To prevent this condition, we add a check to configure that will test
for the presence of linux/mount.h in addition to testing for the mount
fd API. Only if both conditions are met can we actually use the mount
fd API.

Signed-off-by: Markus Mayer <mmayer@broadcom.com>

diff --git a/configure.ac b/configure.ac
index 11b2e155dd2d632ebead69907638082b4c4e05f4..dd582f2a4bd1bafb838d8a0913e2e980ee24ce18 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -389,6 +389,12 @@ AC_CHECK_HEADERS([linux/fs.h ], [], [],
   #endif
 ])
 
+AC_CHECK_HEADERS([linux/mount.h ], [], [],
+ [#ifdef HAVE_LINUX_MOUNT_H
+   # include <linux/mount.h>
+   #endif
+])
+
 AC_CHECK_HEADERS([linux/gsmmux.h ], [], [],
  [#ifdef LINUX_GSMMUX_H
    # include <linux/gsmmux.h>
@@ -479,6 +485,7 @@ have_linux_blkzoned_h=$ac_cv_header_linux_blkzoned_h
 have_linux_btrfs_h=$ac_cv_header_linux_btrfs_h
 have_linux_capability_h=$ac_cv_header_linux_capability_h
 have_linux_kcmp_h=$ac_cv_header_linux_kcmp_h
+have_linux_mount_h=$ac_cv_header_linux_mount_h
 have_linux_pr_h=$ac_cv_header_linux_pr_h
 have_linux_raw_h=$ac_cv_header_linux_raw_h
 have_linux_securebits_h=$ac_cv_header_linux_securebits_h
@@ -1247,6 +1254,7 @@ UL_BUILD_INIT([libmount_mountfd_support])
 UL_REQUIRES_BUILD([libmount_mountfd_support], [libmount])
 UL_REQUIRES_LINUX([libmount_mountfd_support])
 UL_REQUIRES_HAVE([libmount_mountfd_support], [mountfd_api], [mount FDs based API])
+UL_REQUIRES_HAVE([libmount_mountfd_support], [linux_mount_h], [linux/mount.h])
 AS_IF([test "x$build_libmount_mountfd_support" = xyes ], [
   AC_DEFINE([USE_LIBMOUNT_MOUNTFD_SUPPORT], [1], [Enable support for new mount FD based kernel API])
 ])

diff --git a/include/mount-api-utils.h b/include/mount-api-utils.h
index 9044e1cd9d6138849343359437e5a0b863ea117d..8ae546b7ed9f868931891ec0385e4e7423523388 100644 (file)
--- a/include/mount-api-utils.h
+++ b/include/mount-api-utils.h
@@ -5,7 +5,7 @@
 #ifndef UTIL_LINUX_MOUNT_API_UTILS
 #define UTIL_LINUX_MOUNT_API_UTILS
 
-#ifdef HAVE_MOUNTFD_API
+#if defined(HAVE_MOUNTFD_API) && defined(HAVE_LINUX_MOUNT_H)
 
 #include <sys/syscall.h>
 #include <linux/mount.h>
@@ -203,6 +203,6 @@ static inline int fspick(int dfd, const char *pathname, unsigned int flags)
 }
 #endif
 
-#endif /* HAVE_MOUNTFD_API */
+#endif /* HAVE_MOUNTFD_API && HAVE_LINUX_MOUNT_H */
 #endif /* UTIL_LINUX_MOUNT_API_UTILS */
 

diff --git a/libmount/src/hook_idmap.c b/libmount/src/hook_idmap.c
index b3e1d82d4b97f089d17a672762ca3e2680aaed17..9b2425a77defd29e1249a2acf823cb995b53df87 100644 (file)
--- a/libmount/src/hook_idmap.c
+++ b/libmount/src/hook_idmap.c
@@ -33,7 +33,7 @@
 # include <linux/nsfs.h>
 #endif
 
-#ifdef HAVE_MOUNTFD_API
+#if defined(HAVE_MOUNTFD_API) && defined(HAVE_LINUX_MOUNT_H)
 
 typedef enum idmap_type_t {
        ID_TYPE_UID,    /* uidmap entry */
@@ -518,4 +518,4 @@ const struct libmnt_hookset hookset_idmap =
        .deinit = hookset_deinit
 };
 
-#endif /* HAVE_MOUNTFD_API */
+#endif /* HAVE_MOUNTFD_API && HAVE_LINUX_MOUNT_H */

diff --git a/libmount/src/hooks.c b/libmount/src/hooks.c
index 2d7916260587ae76c34faafdeb212b22e727a7e6..dcfe69fa4d46ed027384ce27c937a502d8b018e7 100644 (file)
--- a/libmount/src/hooks.c
+++ b/libmount/src/hooks.c
@@ -46,7 +46,7 @@ static const struct libmnt_hookset *hooksets[] =
        &hookset_mount,
 #endif
        &hookset_mount_legacy,
-#ifdef HAVE_MOUNTFD_API
+#if defined(HAVE_MOUNTFD_API) && defined(HAVE_LINUX_MOUNT_H)
        &hookset_idmap,
 #endif
        &hookset_owner

diff --git a/libmount/src/version.c b/libmount/src/version.c
index 948b1a01de98c2b68a07eb0cd88bcccdc3fa2d67..8e5f165f4920a0eae6aa5042621842ef62deebca 100644 (file)
--- a/libmount/src/version.c
+++ b/libmount/src/version.c
@@ -38,7 +38,7 @@ static const char *lib_features[] = {
 #ifdef USE_LIBMOUNT_SUPPORT_NAMESPACES
        "namespaces",
 #endif
-#ifdef HAVE_MOUNTFD_API
+#if defined(HAVE_MOUNTFD_API) && defined(HAVE_LINUX_MOUNT_H)
        "idmapping",
 #endif
 #ifdef USE_LIBMOUNT_MOUNTFD_SUPPORT