From 6bb1b36726e8a9c8232fc2ec70796817b14d8f8e Mon Sep 17 00:00:00 2001 From: Andrey Ryabinin Date: Fri, 8 Aug 2014 14:22:07 -0700 Subject: [PATCH] lib/idr.c: fix out-of-bounds pointer dereference I'm working on address sanitizer project for kernel. Recently we started experiments with stack instrumentation, to detect out-of-bounds read/write bugs on stack. Just after booting I've hit out-of-bounds read on stack in idr_for_each (and in __idr_remove_all as well): struct idr_layer **paa = &pa[0]; while (id >= 0 && id <= max) { ... while (n < fls(id)) { n += IDR_BITS; p = *--paa; <--- here we are reading pa[-1] value. } } Despite the fact that after this dereference we are exiting out of loop and never use p, such behaviour is undefined and should be avoided. Fix this by moving pointer derference to the beggining of the loop, right before we will use it. Signed-off-by: Andrey Ryabinin Reviewed-by: Lai Jiangshan Cc: Tejun Heo Cc: Alexey Preobrazhensky Cc: Dmitry Vyukov Cc: Konstantin Khlebnikov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Change-Id: Id151fc7e874e3cff64da43eb3359f022de7e6cae Signed-off-by: Seung-Woo Kim --- lib/idr.c | 25 ++++++++++++++----------- 1 file changed, 14 insertions(+), 11 deletions(-) diff --git a/lib/idr.c b/lib/idr.c index a3bfde8..dd06ccb 100644 --- a/lib/idr.c +++ b/lib/idr.c @@ -618,26 +618,27 @@ void __idr_remove_all(struct idr *idp) struct idr_layer **paa = &pa[0]; n = idp->layers * IDR_BITS; - p = idp->top; + *paa = idp->top; rcu_assign_pointer(idp->top, NULL); max = idr_max(idp->layers); id = 0; while (id >= 0 && id <= max) { + p = *paa; while (n > IDR_BITS && p) { n -= IDR_BITS; - *paa++ = p; p = p->ary[(id >> n) & IDR_MASK]; + *++paa = p; } bt_mask = id; id += 1 << n; /* Get the highest bit that the above add changed from 0->1. */ while (n < fls(id ^ bt_mask)) { - if (p) - free_layer(idp, p); + if (*paa) + free_layer(idp, *paa); n += IDR_BITS; - p = *--paa; + --paa; } } idp->layers = 0; @@ -721,15 +722,16 @@ int idr_for_each(struct idr *idp, struct idr_layer **paa = &pa[0]; n = idp->layers * IDR_BITS; - p = rcu_dereference_raw(idp->top); + *paa = rcu_dereference_raw(idp->top); max = idr_max(idp->layers); id = 0; while (id >= 0 && id <= max) { + p = *paa; while (n > 0 && p) { n -= IDR_BITS; - *paa++ = p; p = rcu_dereference_raw(p->ary[(id >> n) & IDR_MASK]); + *++paa = p; } if (p) { @@ -741,7 +743,7 @@ int idr_for_each(struct idr *idp, id += 1 << n; while (n < fls(id)) { n += IDR_BITS; - p = *--paa; + --paa; } } @@ -769,17 +771,18 @@ void *idr_get_next(struct idr *idp, int *nextidp) int n, max; /* find first ent */ - p = rcu_dereference_raw(idp->top); + p = *paa = rcu_dereference_raw(idp->top); if (!p) return NULL; n = (p->layer + 1) * IDR_BITS; max = idr_max(p->layer + 1); while (id >= 0 && id <= max) { + p = *paa; while (n > 0 && p) { n -= IDR_BITS; - *paa++ = p; p = rcu_dereference_raw(p->ary[(id >> n) & IDR_MASK]); + *++paa = p; } if (p) { @@ -797,7 +800,7 @@ void *idr_get_next(struct idr *idp, int *nextidp) id = round_up(id + 1, 1 << n); while (n < fls(id)) { n += IDR_BITS; - p = *--paa; + --paa; } } return NULL; -- 2.7.4