From dd8b477f9a3d8edb136207acb3652e1a34a661b7 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Tue, 1 Jun 2021 11:33:59 +0200 Subject: [PATCH 1/2] mount: Support "nosymfollow" in new mount api Commit dab741e0e02b ("Add a "nosymfollow" mount option.") added support for the "nosymfollow" mount option allowing to block following symlinks when resolving paths. The mount option so far was only available in the old mount api. Make it available in the new mount api as well. Bonus is that it can be applied to a whole subtree not just a single mount. Cc: Christoph Hellwig Cc: Mattias Nissler Cc: Aleksa Sarai Cc: Al Viro Cc: Ross Zwisler Signed-off-by: Christian Brauner --- fs/namespace.c | 9 ++++++--- include/uapi/linux/mount.h | 1 + 2 files changed, 7 insertions(+), 3 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index c3f1a78ba369..ab4174a3c802 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -3464,9 +3464,10 @@ out_type: return ret; } -#define FSMOUNT_VALID_FLAGS \ - (MOUNT_ATTR_RDONLY | MOUNT_ATTR_NOSUID | MOUNT_ATTR_NODEV | \ - MOUNT_ATTR_NOEXEC | MOUNT_ATTR__ATIME | MOUNT_ATTR_NODIRATIME) +#define FSMOUNT_VALID_FLAGS \ + (MOUNT_ATTR_RDONLY | MOUNT_ATTR_NOSUID | MOUNT_ATTR_NODEV | \ + MOUNT_ATTR_NOEXEC | MOUNT_ATTR__ATIME | MOUNT_ATTR_NODIRATIME | \ + MOUNT_ATTR_NOSYMFOLLOW) #define MOUNT_SETATTR_VALID_FLAGS (FSMOUNT_VALID_FLAGS | MOUNT_ATTR_IDMAP) @@ -3487,6 +3488,8 @@ static unsigned int attr_flags_to_mnt_flags(u64 attr_flags) mnt_flags |= MNT_NOEXEC; if (attr_flags & MOUNT_ATTR_NODIRATIME) mnt_flags |= MNT_NODIRATIME; + if (attr_flags & MOUNT_ATTR_NOSYMFOLLOW) + mnt_flags |= MNT_NOSYMFOLLOW; return mnt_flags; } diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h index e6524ead2b7b..dd7a166fdf9c 100644 --- a/include/uapi/linux/mount.h +++ b/include/uapi/linux/mount.h @@ -120,6 +120,7 @@ enum fsconfig_command { #define MOUNT_ATTR_STRICTATIME 0x00000020 /* - Always perform atime updates */ #define MOUNT_ATTR_NODIRATIME 0x00000080 /* Do not update directory access times */ #define MOUNT_ATTR_IDMAP 0x00100000 /* Idmap mount to @userns_fd in struct mount_attr. */ +#define MOUNT_ATTR_NOSYMFOLLOW 0x00200000 /* Do not follow symlinks */ /* * mount_setattr() From 5990b5d770cbfe2b4254d870240e9863aca421e3 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Tue, 1 Jun 2021 11:55:04 +0200 Subject: [PATCH 2/2] tests: test MOUNT_ATTR_NOSYMFOLLOW with mount_setattr() Add tests to verify that MOUNT_ATTR_NOSYMFOLLOW is honored. Cc: Christoph Hellwig Cc: Mattias Nissler Cc: Aleksa Sarai Cc: Al Viro Cc: Ross Zwisler Signed-off-by: Christian Brauner --- .../mount_setattr/mount_setattr_test.c | 88 ++++++++++++++++++- 1 file changed, 85 insertions(+), 3 deletions(-) diff --git a/tools/testing/selftests/mount_setattr/mount_setattr_test.c b/tools/testing/selftests/mount_setattr/mount_setattr_test.c index 4e94e566e040..f31205f04ee0 100644 --- a/tools/testing/selftests/mount_setattr/mount_setattr_test.c +++ b/tools/testing/selftests/mount_setattr/mount_setattr_test.c @@ -136,6 +136,10 @@ struct mount_attr { #define MOUNT_ATTR_IDMAP 0x00100000 #endif +#ifndef MOUNT_ATTR_NOSYMFOLLOW +#define MOUNT_ATTR_NOSYMFOLLOW 0x00200000 +#endif + static inline int sys_mount_setattr(int dfd, const char *path, unsigned int flags, struct mount_attr *attr, size_t size) { @@ -235,6 +239,10 @@ static int prepare_unpriv_mountns(void) return 0; } +#ifndef ST_NOSYMFOLLOW +#define ST_NOSYMFOLLOW 0x2000 /* do not follow symlinks */ +#endif + static int read_mnt_flags(const char *path) { int ret; @@ -245,9 +253,9 @@ static int read_mnt_flags(const char *path) if (ret != 0) return -EINVAL; - if (stat.f_flag & - ~(ST_RDONLY | ST_NOSUID | ST_NODEV | ST_NOEXEC | ST_NOATIME | - ST_NODIRATIME | ST_RELATIME | ST_SYNCHRONOUS | ST_MANDLOCK)) + if (stat.f_flag & ~(ST_RDONLY | ST_NOSUID | ST_NODEV | ST_NOEXEC | + ST_NOATIME | ST_NODIRATIME | ST_RELATIME | + ST_SYNCHRONOUS | ST_MANDLOCK | ST_NOSYMFOLLOW)) return -EINVAL; mnt_flags = 0; @@ -269,6 +277,8 @@ static int read_mnt_flags(const char *path) mnt_flags |= MS_SYNCHRONOUS; if (stat.f_flag & ST_MANDLOCK) mnt_flags |= ST_MANDLOCK; + if (stat.f_flag & ST_NOSYMFOLLOW) + mnt_flags |= ST_NOSYMFOLLOW; return mnt_flags; } @@ -368,8 +378,13 @@ static bool mount_setattr_supported(void) FIXTURE(mount_setattr) { }; +#define NOSYMFOLLOW_TARGET "/mnt/A/AA/data" +#define NOSYMFOLLOW_SYMLINK "/mnt/A/AA/symlink" + FIXTURE_SETUP(mount_setattr) { + int fd = -EBADF; + if (!mount_setattr_supported()) SKIP(return, "mount_setattr syscall not supported"); @@ -412,6 +427,11 @@ FIXTURE_SETUP(mount_setattr) ASSERT_EQ(mount("testing", "/tmp/B/BB", "devpts", MS_RELATIME | MS_NOEXEC | MS_RDONLY, 0), 0); + + fd = creat(NOSYMFOLLOW_TARGET, O_RDWR | O_CLOEXEC); + ASSERT_GT(fd, 0); + ASSERT_EQ(symlink(NOSYMFOLLOW_TARGET, NOSYMFOLLOW_SYMLINK), 0); + ASSERT_EQ(close(fd), 0); } FIXTURE_TEARDOWN(mount_setattr) @@ -1421,4 +1441,66 @@ TEST_F(mount_setattr_idmapped, idmap_mount_tree_invalid) ASSERT_EQ(expected_uid_gid(open_tree_fd, "B/BB/b", 0, 0, 0), 0); } +TEST_F(mount_setattr, mount_attr_nosymfollow) +{ + int fd; + unsigned int old_flags = 0, new_flags = 0, expected_flags = 0; + struct mount_attr attr = { + .attr_set = MOUNT_ATTR_NOSYMFOLLOW, + }; + + if (!mount_setattr_supported()) + SKIP(return, "mount_setattr syscall not supported"); + + fd = open(NOSYMFOLLOW_SYMLINK, O_RDWR | O_CLOEXEC); + ASSERT_GT(fd, 0); + ASSERT_EQ(close(fd), 0); + + old_flags = read_mnt_flags("/mnt/A"); + ASSERT_GT(old_flags, 0); + + ASSERT_EQ(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr)), 0); + + expected_flags = old_flags; + expected_flags |= ST_NOSYMFOLLOW; + + new_flags = read_mnt_flags("/mnt/A"); + ASSERT_EQ(new_flags, expected_flags); + + new_flags = read_mnt_flags("/mnt/A/AA"); + ASSERT_EQ(new_flags, expected_flags); + + new_flags = read_mnt_flags("/mnt/A/AA/B"); + ASSERT_EQ(new_flags, expected_flags); + + new_flags = read_mnt_flags("/mnt/A/AA/B/BB"); + ASSERT_EQ(new_flags, expected_flags); + + fd = open(NOSYMFOLLOW_SYMLINK, O_RDWR | O_CLOEXEC); + ASSERT_LT(fd, 0); + ASSERT_EQ(errno, ELOOP); + + attr.attr_set &= ~MOUNT_ATTR_NOSYMFOLLOW; + attr.attr_clr |= MOUNT_ATTR_NOSYMFOLLOW; + + ASSERT_EQ(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr)), 0); + + expected_flags &= ~ST_NOSYMFOLLOW; + new_flags = read_mnt_flags("/mnt/A"); + ASSERT_EQ(new_flags, expected_flags); + + new_flags = read_mnt_flags("/mnt/A/AA"); + ASSERT_EQ(new_flags, expected_flags); + + new_flags = read_mnt_flags("/mnt/A/AA/B"); + ASSERT_EQ(new_flags, expected_flags); + + new_flags = read_mnt_flags("/mnt/A/AA/B/BB"); + ASSERT_EQ(new_flags, expected_flags); + + fd = open(NOSYMFOLLOW_SYMLINK, O_RDWR | O_CLOEXEC); + ASSERT_GT(fd, 0); + ASSERT_EQ(close(fd), 0); +} + TEST_HARNESS_MAIN