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Subject[PATCH 51/79] namei: remove restrictions on nesting depth
Date
From: Al Viro <viro@zeniv.linux.org.uk>

The only restriction is that on the total amount of symlinks
crossed; how they are nested does not matter

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/namei.c | 66 ++++++++++++++++++++++++++++++++++++++++-----------
include/linux/namei.h | 2 ++
2 files changed, 54 insertions(+), 14 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 8fd8ccb..078db1d 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -492,6 +492,7 @@ void path_put(const struct path *path)
}
EXPORT_SYMBOL(path_put);

+#define EMBEDDED_LEVELS 2
struct nameidata {
struct path path;
union {
@@ -509,9 +510,42 @@ struct nameidata {
struct path link;
void *cookie;
const char *name;
- } stack[MAX_NESTED_LINKS + 1];
+ } *stack, internal[EMBEDDED_LEVELS];
};

+static void set_nameidata(struct nameidata *nd)
+{
+ nd->stack = nd->internal;
+}
+
+static void restore_nameidata(struct nameidata *nd)
+{
+ if (nd->stack != nd->internal) {
+ kfree(nd->stack);
+ nd->stack = nd->internal;
+ }
+}
+
+static int __nd_alloc_stack(struct nameidata *nd)
+{
+ struct saved *p = kmalloc((MAXSYMLINKS + 1) * sizeof(struct saved),
+ GFP_KERNEL);
+ if (unlikely(!p))
+ return -ENOMEM;
+ memcpy(p, nd->internal, sizeof(nd->internal));
+ nd->stack = p;
+ return 0;
+}
+
+static inline int nd_alloc_stack(struct nameidata *nd)
+{
+ if (likely(nd->depth != EMBEDDED_LEVELS - 1))
+ return 0;
+ if (likely(nd->stack != nd->internal))
+ return 0;
+ return __nd_alloc_stack(nd);
+}
+
/*
* Path walking has 2 modes, rcu-walk and ref-walk (see
* Documentation/filesystems/path-lookup.txt). In situations when we can't
@@ -857,7 +891,7 @@ const char *get_link(struct nameidata *nd)
if (nd->link.mnt == nd->path.mnt)
mntget(nd->link.mnt);

- if (unlikely(current->total_link_count >= 40)) {
+ if (unlikely(current->total_link_count >= MAXSYMLINKS)) {
path_put(&nd->path);
path_put(&nd->link);
return ERR_PTR(-ELOOP);
@@ -1781,22 +1815,18 @@ Walked:
if (err) {
const char *s;

- if (unlikely(current->link_count >= MAX_NESTED_LINKS)) {
- path_put_conditional(&nd->link, nd);
- path_put(&nd->path);
- err = -ELOOP;
- goto Err;
+ err = nd_alloc_stack(nd);
+ if (unlikely(err)) {
+ path_to_nameidata(&nd->link, nd);
+ break;
}
- BUG_ON(nd->depth >= MAX_NESTED_LINKS);

nd->depth++;
- current->link_count++;

s = get_link(nd);

if (unlikely(IS_ERR(s))) {
err = PTR_ERR(s);
- current->link_count--;
nd->depth--;
goto Err;
}
@@ -1804,7 +1834,6 @@ Walked:
if (unlikely(!s)) {
/* jumped */
put_link(nd);
- current->link_count--;
nd->depth--;
} else {
if (*s == '/') {
@@ -1834,7 +1863,6 @@ Walked:
Err:
while (unlikely(nd->depth)) {
put_link(nd);
- current->link_count--;
nd->depth--;
}
return err;
@@ -1843,7 +1871,6 @@ OK:
name = nd->stack[nd->depth].name;
err = walk_component(nd, LOOKUP_FOLLOW);
put_link(nd);
- current->link_count--;
nd->depth--;
goto Walked;
}
@@ -2047,7 +2074,11 @@ static int path_lookupat(int dfd, const struct filename *name,
static int filename_lookup(int dfd, struct filename *name,
unsigned int flags, struct nameidata *nd)
{
- int retval = path_lookupat(dfd, name, flags | LOOKUP_RCU, nd);
+ int retval;
+
+ set_nameidata(nd);
+ retval = path_lookupat(dfd, name, flags | LOOKUP_RCU, nd);
+
if (unlikely(retval == -ECHILD))
retval = path_lookupat(dfd, name, flags, nd);
if (unlikely(retval == -ESTALE))
@@ -2055,6 +2086,7 @@ static int filename_lookup(int dfd, struct filename *name,

if (likely(!retval))
audit_inode(name, nd->path.dentry, flags & LOOKUP_PARENT);
+ restore_nameidata(nd);
return retval;
}

@@ -2385,6 +2417,7 @@ filename_mountpoint(int dfd, struct filename *name, struct path *path,
int error;
if (IS_ERR(name))
return PTR_ERR(name);
+ set_nameidata(&nd);
error = path_mountpoint(dfd, name, path, &nd, flags | LOOKUP_RCU);
if (unlikely(error == -ECHILD))
error = path_mountpoint(dfd, name, path, &nd, flags);
@@ -2392,6 +2425,7 @@ filename_mountpoint(int dfd, struct filename *name, struct path *path,
error = path_mountpoint(dfd, name, path, &nd, flags | LOOKUP_REVAL);
if (likely(!error))
audit_inode(name, path->dentry, 0);
+ restore_nameidata(&nd);
putname(name);
return error;
}
@@ -3281,11 +3315,13 @@ struct file *do_filp_open(int dfd, struct filename *pathname,
int flags = op->lookup_flags;
struct file *filp;

+ set_nameidata(&nd);
filp = path_openat(dfd, pathname, &nd, op, flags | LOOKUP_RCU);
if (unlikely(filp == ERR_PTR(-ECHILD)))
filp = path_openat(dfd, pathname, &nd, op, flags);
if (unlikely(filp == ERR_PTR(-ESTALE)))
filp = path_openat(dfd, pathname, &nd, op, flags | LOOKUP_REVAL);
+ restore_nameidata(&nd);
return filp;
}

@@ -3299,6 +3335,7 @@ struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt,

nd.root.mnt = mnt;
nd.root.dentry = dentry;
+ set_nameidata(&nd);

if (d_is_symlink(dentry) && op->intent & LOOKUP_OPEN)
return ERR_PTR(-ELOOP);
@@ -3312,6 +3349,7 @@ struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt,
file = path_openat(-1, filename, &nd, op, flags);
if (unlikely(file == ERR_PTR(-ESTALE)))
file = path_openat(-1, filename, &nd, op, flags | LOOKUP_REVAL);
+ restore_nameidata(&nd);
putname(filename);
return file;
}
diff --git a/include/linux/namei.h b/include/linux/namei.h
index a5d5bed..3a6cc96 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -11,6 +11,8 @@ struct nameidata;

enum { MAX_NESTED_LINKS = 8 };

+#define MAXSYMLINKS 40
+
/*
* Type of the last component on LOOKUP_PARENT
*/
--
2.1.4


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