From 4c7d0c9cb713a28b133b265d595de2a93ee09712 Mon Sep 17 00:00:00 2001 From: Amir Goldstein Date: Wed, 18 Jan 2017 15:19:54 +0100 Subject: [PATCH] ovl: fix possible use after free on redirect dir lookup ovl_lookup_layer() iterates on path elements of d->name.name but also frees and allocates a new pointer for d->name.name. For the case of lookup in upper layer, the initial d->name.name pointer is stable (dentry->d_name), but for lower layers, the initial d->name.name can be d->redirect, which can be freed during iteration. [SzM] Keep the count of remaining characters in the redirect path and calculate the current position from that. This works becuase only the prefix is modified, the ending always stays the same. Fixes: 02b69b284cd7 ("ovl: lookup redirects") Signed-off-by: Amir Goldstein Signed-off-by: Miklos Szeredi --- fs/overlayfs/namei.c | 27 ++++++++++++++++++--------- 1 file changed, 18 insertions(+), 9 deletions(-) diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c index 9ad48d9202a9..023bb0b03352 100644 --- a/fs/overlayfs/namei.c +++ b/fs/overlayfs/namei.c @@ -154,29 +154,38 @@ out_err: static int ovl_lookup_layer(struct dentry *base, struct ovl_lookup_data *d, struct dentry **ret) { - const char *s = d->name.name; + /* Counting down from the end, since the prefix can change */ + size_t rem = d->name.len - 1; struct dentry *dentry = NULL; int err; - if (*s != '/') + if (d->name.name[0] != '/') return ovl_lookup_single(base, d, d->name.name, d->name.len, 0, "", ret); - while (*s++ == '/' && !IS_ERR_OR_NULL(base) && d_can_lookup(base)) { + while (!IS_ERR_OR_NULL(base) && d_can_lookup(base)) { + const char *s = d->name.name + d->name.len - rem; const char *next = strchrnul(s, '/'); - size_t slen = strlen(s); + size_t thislen = next - s; + bool end = !next[0]; - if (WARN_ON(slen > d->name.len) || - WARN_ON(strcmp(d->name.name + d->name.len - slen, s))) + /* Verify we did not go off the rails */ + if (WARN_ON(s[-1] != '/')) return -EIO; - err = ovl_lookup_single(base, d, s, next - s, - d->name.len - slen, next, &base); + err = ovl_lookup_single(base, d, s, thislen, + d->name.len - rem, next, &base); dput(dentry); if (err) return err; dentry = base; - s = next; + if (end) + break; + + rem -= thislen + 1; + + if (WARN_ON(rem >= d->name.len)) + return -EIO; } *ret = dentry; return 0; -- 2.39.5