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cifs: build_path_from_dentry() race fix 

deal with d_move() races properly; rename_lock read-retry loop,
rcu_read_lock() held while walking to root, d_lock held over
subtraction from namelen and copying the component to stabilize
->d_name.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2011-07-16 23:37:20 -04:00
parent 3110df800c
commit dc137bf553
1 changed files with 12 additions and 1 deletions
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13
fs/cifs/dir.c
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@ -55,6 +55,7 @@ build_path_from_dentry(struct dentry *direntry)
char dirsep;
struct cifs_sb_info *cifs_sb = CIFS_SB(direntry->d_sb);
struct cifs_tcon *tcon = cifs_sb_master_tcon(cifs_sb);
unsigned seq;
if (direntry == NULL)
return NULL; /* not much we can do if dentry is freed and
@ -68,22 +69,29 @@ build_path_from_dentry(struct dentry *direntry)
dfsplen = 0;
cifs_bp_rename_retry:
namelen = dfsplen;
seq = read_seqbegin(&rename_lock);
rcu_read_lock();
for (temp = direntry; !IS_ROOT(temp);) {
namelen += (1 + temp->d_name.len);
temp = temp->d_parent;
if (temp == NULL) {
cERROR(1, "corrupt dentry");
rcu_read_unlock();
return NULL;
}
}
rcu_read_unlock();
full_path = kmalloc(namelen+1, GFP_KERNEL);
if (full_path == NULL)
return full_path;
full_path[namelen] = 0; /* trailing null */
rcu_read_lock();
for (temp = direntry; !IS_ROOT(temp);) {
spin_lock(&temp->d_lock);
namelen -= 1 + temp->d_name.len;
if (namelen < 0) {
spin_unlock(&temp->d_lock);
break;
} else {
full_path[namelen] = dirsep;
@ -91,14 +99,17 @@ cifs_bp_rename_retry:
temp->d_name.len);
cFYI(0, "name: %s", full_path + namelen);
}
spin_unlock(&temp->d_lock);
temp = temp->d_parent;
if (temp == NULL) {
cERROR(1, "corrupt dentry");
rcu_read_unlock();
kfree(full_path);
return NULL;
}
}
if (namelen != dfsplen) {
rcu_read_unlock();
if (namelen != dfsplen || read_seqretry(&rename_lock, seq)) {
cERROR(1, "did not end path lookup where expected namelen is %d",
namelen);
/* presumably this is only possible if racing with a rename