[IPV4]: severe locking bug in fib_semantics.c

Found in 2.4 by Yixin Pan <yxpan@hotmail.com>.

> When I read fib_semantics.c of Linux-2.4.32, write_lock(&fib_info_lock) =
> is used in fib_release_info() instead of write_lock_bh(&fib_info_lock).  =
> Is the following case possible: a BH interrupts fib_release_info() while =
> holding the write lock, and calls ip_check_fib_default() which calls =
> read_lock(&fib_info_lock), and spin forever.

Signed-off-by: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 9be53a8..5173800 100644 (file)
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -159,7 +159,7 @@ void free_fib_info(struct fib_info *fi)
 
 void fib_release_info(struct fib_info *fi)
 {
-       write_lock(&fib_info_lock);
+       write_lock_bh(&fib_info_lock);
        if (fi && --fi->fib_treeref == 0) {
                hlist_del(&fi->fib_hash);
                if (fi->fib_prefsrc)
@@ -172,7 +172,7 @@ void fib_release_info(struct fib_info *fi)
                fi->fib_dead = 1;
                fib_info_put(fi);
        }
-       write_unlock(&fib_info_lock);
+       write_unlock_bh(&fib_info_lock);
 }
 
 static __inline__ int nh_comp(const struct fib_info *fi, const struct fib_info *ofi)
@@ -598,7 +598,7 @@ static void fib_hash_move(struct hlist_head *new_info_hash,
        unsigned int old_size = fib_hash_size;
        unsigned int i, bytes;
 
-       write_lock(&fib_info_lock);
+       write_lock_bh(&fib_info_lock);
        old_info_hash = fib_info_hash;
        old_laddrhash = fib_info_laddrhash;
        fib_hash_size = new_size;
@@ -639,7 +639,7 @@ static void fib_hash_move(struct hlist_head *new_info_hash,
        }
        fib_info_laddrhash = new_laddrhash;
 
-       write_unlock(&fib_info_lock);
+       write_unlock_bh(&fib_info_lock);
 
        bytes = old_size * sizeof(struct hlist_head *);
        fib_hash_free(old_info_hash, bytes);
@@ -820,7 +820,7 @@ link_it:
 
        fi->fib_treeref++;
        atomic_inc(&fi->fib_clntref);
-       write_lock(&fib_info_lock);
+       write_lock_bh(&fib_info_lock);
        hlist_add_head(&fi->fib_hash,
                       &fib_info_hash[fib_info_hashfn(fi)]);
        if (fi->fib_prefsrc) {
@@ -839,7 +839,7 @@ link_it:
                head = &fib_info_devhash[hash];
                hlist_add_head(&nh->nh_hash, head);
        } endfor_nexthops(fi)
-       write_unlock(&fib_info_lock);
+       write_unlock_bh(&fib_info_lock);
        return fi;
 
 err_inval: