linux-kernel - [PATCH] lib/stackdepot.c: fix a condition in stack_depot

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Message-ID: <20200312113006.GA20562@mwanda>
Date:   Thu, 12 Mar 2020 14:30:06 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Miles Chen <miles.chen@...iatek.com>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: [PATCH] lib/stackdepot.c: fix a condition in stack_depot_fetch()

We should check for a NULL pointer first before adding the offset.
Otherwise if the pointer is NULL and the offset is non-zero, it will
lead to an Oops.

Fixes: d45048e65a59 ("lib/stackdepot.c: check depot_index before accessing the stack slab")
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
---
 lib/stackdepot.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index da5d1880bf34..2caffc64e4c8 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -207,18 +207,16 @@ unsigned int stack_depot_fetch(depot_stack_handle_t handle,
 	size_t offset = parts.offset << STACK_ALLOC_ALIGN;
 	struct stack_record *stack;
 
+	*entries = NULL;
 	if (parts.slabindex > depot_index) {
 		WARN(1, "slab index %d out of bounds (%d) for stack id %08x\n",
 			parts.slabindex, depot_index, handle);
-		*entries = NULL;
 		return 0;
 	}
 	slab = stack_slabs[parts.slabindex];
-	stack = slab + offset;
-	if (!stack) {
-		*entries = NULL;
+	if (!slab)
 		return 0;
-	}
+	stack = slab + offset;
 
 	*entries = stack->entries;
 	return stack->size;
-- 
2.20.1