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From 2cc9d436e80632157b99e18d413a62b2d44d321a Mon Sep 17 00:00:00 2001
From: Ron Yorston <rmy@pobox.com>
Date: Tue, 22 Aug 2023 09:38:03 +0100
Subject: tsort: avoid use-after-free
When the input data contained a cycle it was possible for tsort to
attempt to access freed nodes. This sometimes resulted in the
test case 'echo a b b a | tsort' crashing.
Don't free nodes when they're removed from the graph.
function old new delta
tsort_main 621 596 -25
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-25) Total: -25 bytes
Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
---
coreutils/tsort.c | 20 +++++++++++++++++---
1 file changed, 17 insertions(+), 3 deletions(-)
diff --git a/coreutils/tsort.c b/coreutils/tsort.c
index a451ed2ff..e1ee6bcd7 100644
--- a/coreutils/tsort.c
+++ b/coreutils/tsort.c
@@ -101,6 +101,10 @@ int tsort_main(int argc UNUSED_PARAM, char **argv)
ssize_t len;
struct node *a;
int cycles;
+ unsigned i;
+#if ENABLE_FEATURE_CLEAN_UP
+ unsigned max_len;
+#endif
INIT_G();
@@ -152,9 +156,11 @@ int tsort_main(int argc UNUSED_PARAM, char **argv)
* - if any nodes are left, they form cycles.
*/
cycles = 0;
+#if ENABLE_FEATURE_CLEAN_UP
+ max_len = G.nodes_len;
+#endif
while (G.nodes_len) {
struct node *n;
- unsigned i;
/* Search for first node with no incoming edges */
for (i = 0; i < G.nodes_len; i++) {
@@ -173,16 +179,24 @@ int tsort_main(int argc UNUSED_PARAM, char **argv)
/* Remove the node (need no longer maintain sort) */
n = G.nodes[i];
G.nodes[i] = G.nodes[--G.nodes_len];
+#if ENABLE_FEATURE_CLEAN_UP
+ /* Keep reference to removed node so it can be freed */
+ G.nodes[G.nodes_len] = n;
+#endif
/* And remove its outgoing edges */
for (i = 0; i < n->out_count; i++)
n->out[i]->in_count--;
- free(n->out);
puts(n->name);
- free(n);
+ }
+#if ENABLE_FEATURE_CLEAN_UP
+ for (i = 0; i < max_len; i++) {
+ free(G.nodes[i]->out);
+ free(G.nodes[i]);
}
free(G.nodes);
+#endif
fflush_stdout_and_exit(cycles ? 1 : 0);
}
--
cgit v1.2.3
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