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authorAl Viro <viro@zeniv.linux.org.uk>2020-01-19 11:44:51 -0500
committerAl Viro <viro@zeniv.linux.org.uk>2020-03-13 21:08:19 -0400
commitb4c0353693d22f9dcfa4757262dab0aab8376d19 (patch)
tree1449c03091a907b391db729c0b29ac98b5129e36 /fs/namei.c
parentad6cc4c338f4e5124c29971ea749073a697063a1 (diff)
sanitize handling of nd->last_type, kill LAST_BIND
->last_type values are set in 3 places: path_init() (sets to LAST_ROOT), link_path_walk (LAST_NORM/DOT/DOTDOT) and pick_link (LAST_BIND). The are checked in walk_component(), lookup_last() and do_last(). They also get copied to the caller by filename_parentat(). In the last 3 cases the value is what we had at the return from link_path_walk(). In case of walk_component() it's either directly downstream from assignment in link_path_walk() or, when called by lookup_last(), the value we have at the return from link_path_walk(). The value at the entry into link_path_walk() can survive to return only if the pathname contains nothing but slashes. Note that pick_link() never returns such - pure jumps are handled directly. So for the calls of link_path_walk() for trailing symlinks it does not matter what value had been there at the entry; the value at the return won't depend upon it. There are 3 call chains that might have pick_link() storing LAST_BIND: 1) pick_link() from step_into() from walk_component() from link_path_walk(). In that case we will either be parsing the next component immediately after return into link_path_walk(), which will overwrite the ->last_type before anyone has a chance to look at it, or we'll fail, in which case nobody will be looking at ->last_type at all. 2) pick_link() from step_into() from walk_component() from lookup_last(). The value is never looked at due to the above; it won't affect the value seen at return from any link_path_walk(). 3) pick_link() from step_into() from do_last(). Ditto. In other words, assignemnt in pick_link() is pointless, and so is LAST_BIND itself; nothing ever looks at that value. Kill it off. And make link_path_walk() _always_ assign ->last_type - in the only case when the value at the entry might survive to the return that value is always LAST_ROOT, inherited from path_init(). Move that assignment from path_init() into the beginning of link_path_walk(), to consolidate the things. Historical note: LAST_BIND used to be used for the kludge with trailing pure jump symlinks (extra iteration through the top-level loop). No point keeping it anymore... Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/namei.c')
-rw-r--r--fs/namei.c3
1 files changed, 1 insertions, 2 deletions
diff --git a/fs/namei.c b/fs/namei.c
index 02f148124831..1a83641e95e6 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1785,7 +1785,6 @@ static const char *pick_link(struct nameidata *nd, struct path *link,
if (unlikely(error))
return ERR_PTR(error);
- nd->last_type = LAST_BIND;
res = READ_ONCE(inode->i_link);
if (!res) {
const char * (*get)(struct dentry *, struct inode *,
@@ -2123,6 +2122,7 @@ static int link_path_walk(const char *name, struct nameidata *nd)
{
int err;
+ nd->last_type = LAST_ROOT;
if (IS_ERR(name))
return PTR_ERR(name);
while (*name=='/')
@@ -2224,7 +2224,6 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
if (flags & LOOKUP_RCU)
rcu_read_lock();
- nd->last_type = LAST_ROOT; /* if there are only slashes... */
nd->flags = flags | LOOKUP_JUMPED | LOOKUP_PARENT;
nd->depth = 0;