From 26992852dde78e6acc9a9b2bdc9e734428e34d65 Mon Sep 17 00:00:00 2001 From: Sonny Rao Date: Sun, 25 Jun 2006 05:49:34 -0700 Subject: [PATCH] [PATCH] idr: fix race in idr code From: Sonny Rao I ran into a bug where the kernel died in the idr code: cpu 0x1d: Vector: 300 (Data Access) at [c000000b7096f710] pc: c0000000001f8984: .idr_get_new_above_int+0x140/0x330 lr: c0000000001f89b4: .idr_get_new_above_int+0x170/0x330 sp: c000000b7096f990 msr: 800000000000b032 dar: 0 dsisr: 40010000 current = 0xc000000b70d43830 paca = 0xc000000000556900 pid = 2022, comm = hwup 1d:mon> t [c000000b7096f990] c0000000000d2ad8 .expand_files+0x2e8/0x364 (unreliable) [c000000b7096faa0] c0000000001f8bf8 .idr_get_new_above+0x18/0x68 [c000000b7096fb20] c00000000002a054 .init_new_context+0x5c/0xf0 [c000000b7096fbc0] c000000000049dc8 .copy_process+0x91c/0x1404 [c000000b7096fcd0] c00000000004a988 .do_fork+0xd8/0x224 [c000000b7096fdc0] c00000000000ebdc .sys_clone+0x5c/0x74 [c000000b7096fe30] c000000000008950 .ppc_clone+0x8/0xc -- Exception: c00 (System Call) at 000000000fde887c SP (f8b4e7a0) is in userspace Turned out to be a race-condition and NULL ptr deref, here's my fix: Users of the idr code are supposed to call idr_pre_get without locking, so the idr code must serialize itself with respect to layer allocations. However, it fails to do so in an error path in idr_get_new_above_int(). I added the missing locking to fix this. Signed-off-by: Sonny Rao Cc: Signed-off-by: Andrew Morton Signed-off-by: Chris Wright --- lib/idr.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/lib/idr.c b/lib/idr.c index d226259c3c28..de19030a999b 100644 --- a/lib/idr.c +++ b/lib/idr.c @@ -48,15 +48,21 @@ static struct idr_layer *alloc_layer(struct idr *idp) return(p); } +/* only called when idp->lock is held */ +static void __free_layer(struct idr *idp, struct idr_layer *p) +{ + p->ary[0] = idp->id_free; + idp->id_free = p; + idp->id_free_cnt++; +} + static void free_layer(struct idr *idp, struct idr_layer *p) { /* * Depends on the return element being zeroed. */ spin_lock(&idp->lock); - p->ary[0] = idp->id_free; - idp->id_free = p; - idp->id_free_cnt++; + __free_layer(idp, p); spin_unlock(&idp->lock); } @@ -184,12 +190,14 @@ build_up: * The allocation failed. If we built part of * the structure tear it down. */ + spin_lock(&idp->lock); for (new = p; p && p != idp->top; new = p) { p = p->ary[0]; new->ary[0] = NULL; new->bitmap = new->count = 0; - free_layer(idp, new); + __free_layer(idp, new); } + spin_unlock(&idp->lock); return -1; } new->ary[0] = p; -- 2.39.5