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authorJan Kara <jack@suse.cz>2010-09-15 17:38:58 +0200
committerJan Kara <jack@suse.cz>2011-01-12 19:14:55 +0100
commitf00c9e44ad1a9660fe8cd3ca15b6cd9497172eab (patch)
treecbb47ae0d8aba9d8b3c44714b000156715cdf969 /fs/quota
parent4162cf64973df51fc885825bc9ca4d055891c49f (diff)
downloadlinaro-lsk-f00c9e44ad1a9660fe8cd3ca15b6cd9497172eab.tar.gz
quota: Fix deadlock during path resolution
As Al Viro pointed out path resolution during Q_QUOTAON calls to quotactl is prone to deadlocks. We hold s_umount semaphore for reading during the path resolution and resolution itself may need to acquire the semaphore for writing when e. g. autofs mountpoint is passed. Solve the problem by performing the resolution before we get hold of the superblock (and thus s_umount semaphore). The whole thing is complicated by the fact that some filesystems (OCFS2) ignore the path argument. So to distinguish between filesystem which want the path and which do not we introduce new .quota_on_meta callback which does not get the path. OCFS2 then uses this callback instead of old .quota_on. CC: Al Viro <viro@ZenIV.linux.org.uk> CC: Christoph Hellwig <hch@lst.de> CC: Ted Ts'o <tytso@mit.edu> CC: Joel Becker <joel.becker@oracle.com> Signed-off-by: Jan Kara <jack@suse.cz>
Diffstat (limited to 'fs/quota')
-rw-r--r--fs/quota/dquot.c18
-rw-r--r--fs/quota/quota.c41
2 files changed, 29 insertions, 30 deletions
diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index 84becd3e477..a2a622e079f 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -2189,8 +2189,8 @@ int dquot_resume(struct super_block *sb, int type)
}
EXPORT_SYMBOL(dquot_resume);
-int dquot_quota_on_path(struct super_block *sb, int type, int format_id,
- struct path *path)
+int dquot_quota_on(struct super_block *sb, int type, int format_id,
+ struct path *path)
{
int error = security_quota_on(path->dentry);
if (error)
@@ -2204,20 +2204,6 @@ int dquot_quota_on_path(struct super_block *sb, int type, int format_id,
DQUOT_LIMITS_ENABLED);
return error;
}
-EXPORT_SYMBOL(dquot_quota_on_path);
-
-int dquot_quota_on(struct super_block *sb, int type, int format_id, char *name)
-{
- struct path path;
- int error;
-
- error = kern_path(name, LOOKUP_FOLLOW, &path);
- if (!error) {
- error = dquot_quota_on_path(sb, type, format_id, &path);
- path_put(&path);
- }
- return error;
-}
EXPORT_SYMBOL(dquot_quota_on);
/*
diff --git a/fs/quota/quota.c b/fs/quota/quota.c
index b299961e1ed..b34bdb25490 100644
--- a/fs/quota/quota.c
+++ b/fs/quota/quota.c
@@ -64,18 +64,15 @@ static int quota_sync_all(int type)
}
static int quota_quotaon(struct super_block *sb, int type, int cmd, qid_t id,
- void __user *addr)
+ struct path *path)
{
- char *pathname;
- int ret = -ENOSYS;
-
- pathname = getname(addr);
- if (IS_ERR(pathname))
- return PTR_ERR(pathname);
- if (sb->s_qcop->quota_on)
- ret = sb->s_qcop->quota_on(sb, type, id, pathname);
- putname(pathname);
- return ret;
+ if (!sb->s_qcop->quota_on && !sb->s_qcop->quota_on_meta)
+ return -ENOSYS;
+ if (sb->s_qcop->quota_on_meta)
+ return sb->s_qcop->quota_on_meta(sb, type, id);
+ if (IS_ERR(path))
+ return PTR_ERR(path);
+ return sb->s_qcop->quota_on(sb, type, id, path);
}
static int quota_getfmt(struct super_block *sb, int type, void __user *addr)
@@ -241,7 +238,7 @@ static int quota_getxquota(struct super_block *sb, int type, qid_t id,
/* Copy parameters and call proper function */
static int do_quotactl(struct super_block *sb, int type, int cmd, qid_t id,
- void __user *addr)
+ void __user *addr, struct path *path)
{
int ret;
@@ -256,7 +253,7 @@ static int do_quotactl(struct super_block *sb, int type, int cmd, qid_t id,
switch (cmd) {
case Q_QUOTAON:
- return quota_quotaon(sb, type, cmd, id, addr);
+ return quota_quotaon(sb, type, cmd, id, path);
case Q_QUOTAOFF:
if (!sb->s_qcop->quota_off)
return -ENOSYS;
@@ -335,6 +332,7 @@ SYSCALL_DEFINE4(quotactl, unsigned int, cmd, const char __user *, special,
{
uint cmds, type;
struct super_block *sb = NULL;
+ struct path path, *pathp = NULL;
int ret;
cmds = cmd >> SUBCMDSHIFT;
@@ -351,12 +349,27 @@ SYSCALL_DEFINE4(quotactl, unsigned int, cmd, const char __user *, special,
return -ENODEV;
}
+ /*
+ * Path for quotaon has to be resolved before grabbing superblock
+ * because that gets s_umount sem which is also possibly needed by path
+ * resolution (think about autofs) and thus deadlocks could arise.
+ */
+ if (cmds == Q_QUOTAON) {
+ ret = user_path_at(AT_FDCWD, addr, LOOKUP_FOLLOW, &path);
+ if (ret)
+ pathp = ERR_PTR(ret);
+ else
+ pathp = &path;
+ }
+
sb = quotactl_block(special);
if (IS_ERR(sb))
return PTR_ERR(sb);
- ret = do_quotactl(sb, type, cmds, id, addr);
+ ret = do_quotactl(sb, type, cmds, id, addr, pathp);
drop_super(sb);
+ if (pathp && !IS_ERR(pathp))
+ path_put(pathp);
return ret;
}