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authorAl Viro <viro@zeniv.linux.org.uk>2010-08-09 12:05:43 -0400
committerGreg Kroah-Hartman <gregkh@suse.de>2010-08-13 13:30:50 -0700
commit752638f5e4285a42b2df0394c060054f7154c85e (patch)
tree8768767c6472eded20ca5f4d1fb501e6e5a6c074
parent252eca4afb1580b80bac2fd19138818e59980873 (diff)
downloadlinux-2.6.34-ux500-752638f5e4285a42b2df0394c060054f7154c85e.tar.gz
Fix sget() race with failing mount
commit 7a4dec53897ecd3367efb1e12fe8a4edc47dc0e9 upstream. If sget() finds a matching superblock being set up, it'll grab an active reference to it and grab s_umount. That's fine - we'll wait for completion of foofs_get_sb() that way. However, if said foofs_get_sb() fails we'll end up holding the halfway-created superblock. deactivate_locked_super() called by foofs_get_sb() will just unlock the sucker since we are holding another active reference to it. What we need is a way to tell if superblock has been successfully set up. Unfortunately, neither ->s_root nor the check for MS_ACTIVE quite fit. Cheap and easy way, suitable for backport: new flag set by the (only) caller of ->get_sb(). If that flag isn't present by the time sget() grabbed s_umount on preexisting superblock it has found, it's seeing a stillborn and should just bury it with deactivate_locked_super() (and repeat the search). Longer term we want to set that flag in ->get_sb() instances (and check for it to distinguish between "sget() found us a live sb" and "sget() has allocated an sb, we need to set it up" in there, instead of checking ->s_root as we do now). Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r--fs/namespace.c2
-rw-r--r--fs/super.c6
-rw-r--r--include/linux/fs.h1
3 files changed, 8 insertions, 1 deletions
diff --git a/fs/namespace.c b/fs/namespace.c
index 88058de59c7..32dcd24bbc9 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1984,7 +1984,7 @@ long do_mount(char *dev_name, char *dir_name, char *type_page,
if (flags & MS_RDONLY)
mnt_flags |= MNT_READONLY;
- flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE |
+ flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | MS_BORN |
MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT |
MS_STRICTATIME);
diff --git a/fs/super.c b/fs/super.c
index 938119ab8dc..c7765bd38ee 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -305,8 +305,13 @@ retry:
if (s) {
up_write(&s->s_umount);
destroy_super(s);
+ s = NULL;
}
down_write(&old->s_umount);
+ if (unlikely(!(old->s_flags & MS_BORN))) {
+ deactivate_locked_super(old);
+ goto retry;
+ }
return old;
}
}
@@ -909,6 +914,7 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void
goto out_free_secdata;
BUG_ON(!mnt->mnt_sb);
WARN_ON(!mnt->mnt_sb->s_bdi);
+ mnt->mnt_sb->s_flags |= MS_BORN;
error = security_sb_kern_mount(mnt->mnt_sb, flags, secdata);
if (error)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 68ca1b0491a..3cdaa57862c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -209,6 +209,7 @@ struct inodes_stat_t {
#define MS_KERNMOUNT (1<<22) /* this is a kern_mount call */
#define MS_I_VERSION (1<<23) /* Update inode I_version field */
#define MS_STRICTATIME (1<<24) /* Always perform atime updates */
+#define MS_BORN (1<<29)
#define MS_ACTIVE (1<<30)
#define MS_NOUSER (1<<31)