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Btrfs: avoid possible use-after-free in clear_extent_bit()

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clear_extent_bit()
{
    next_node = rb_next(&state->rb_node);
    ...
    clear_state_bit(state);  <-- this may free next_node
    if (next_node) {
        state = rb_entry(next_node);
        ...
    }
}

clear_state_bit() calls merge_state() which may free the next node
of the passing extent_state, so clear_extent_bit() may end up
referencing freed memory.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
This commit is contained in:
Li Zefan 2012-03-12 16:39:48 +08:00 committed by David Sterba
parent 8e52acf704
commit cdc6a39525
1 changed files with 21 additions and 15 deletions
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36
fs/btrfs/extent_io.c
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@ -402,6 +402,15 @@ static int split_state(struct extent_io_tree *tree, struct extent_state *orig,
return 0;
}
static struct extent_state *next_state(struct extent_state *state)
{
struct rb_node *next = rb_next(&state->rb_node);
if (next)
return rb_entry(next, struct extent_state, rb_node);
else
return NULL;
}
/*
* utility function to clear some bits in an extent state struct.
* it will optionally wake up any one waiting on this state (wake == 1)
@ -409,10 +418,11 @@ static int split_state(struct extent_io_tree *tree, struct extent_state *orig,
* If no bits are set on the state struct after clearing things, the
* struct is freed and removed from the tree
*/
static void clear_state_bit(struct extent_io_tree *tree,
struct extent_state *state,
int *bits, int wake)
static struct extent_state *clear_state_bit(struct extent_io_tree *tree,
struct extent_state *state,
int *bits, int wake)
{
struct extent_state *next;
int bits_to_clear = *bits & ~EXTENT_CTLBITS;
if ((bits_to_clear & EXTENT_DIRTY) && (state->state & EXTENT_DIRTY)) {
@ -425,6 +435,7 @@ static void clear_state_bit(struct extent_io_tree *tree,
if (wake)
wake_up(&state->wq);
if (state->state == 0) {
next = next_state(state);
if (state->tree) {
rb_erase(&state->rb_node, &tree->state);
state->tree = NULL;
@ -434,7 +445,9 @@ static void clear_state_bit(struct extent_io_tree *tree,
}
} else {
merge_state(tree, state);
next = next_state(state);
}
return next;
}
static struct extent_state *
@ -473,7 +486,6 @@ int clear_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
struct extent_state *state;
struct extent_state *cached;
struct extent_state *prealloc = NULL;
struct rb_node *next_node;
struct rb_node *node;
u64 last_end;
int err;
@ -525,14 +537,11 @@ hit_next:
WARN_ON(state->end < start);
last_end = state->end;
if (state->end < end && !need_resched())
next_node = rb_next(&state->rb_node);
else
next_node = NULL;
/* the state doesn't have the wanted bits, go ahead */
if (!(state->state & bits))
if (!(state->state & bits)) {
state = next_state(state);
goto next;
}
/*
* | ---- desired range ---- |
@ -590,16 +599,13 @@ hit_next:
goto out;
}
clear_state_bit(tree, state, &bits, wake);
state = clear_state_bit(tree, state, &bits, wake);
next:
if (last_end == (u64)-1)
goto out;
start = last_end + 1;
if (start <= end && next_node) {
state = rb_entry(next_node, struct extent_state,
rb_node);
if (start <= end && state && !need_resched())
goto hit_next;
}
goto search_again;
out: