print_entries() uses n_entries both as the number of sort entries and as
its own return value, so the -ENOMEM it stores when the stats allocation
fails overwrites the count that the cleanup still needs:
n_entries = tracing_map_sort_entries(map, ...);
if (n_entries < 0)
return n_entries;
...
if (!stats) {
n_entries = -ENOMEM;
goto out;
}
...
out:
tracing_map_destroy_sort_entries(sort_entries, n_entries);
tracing_map_destroy_sort_entries() takes an unsigned int and loops up to
it, so -ENOMEM arrives as 4294967284. It walks an array of at most
map->max_elts pointers and calls destroy_sort_entry(), which dereferences
and frees, on whatever lies past the end.
Reading the hist file of a trigger with a .percent value, with that
allocation forced to fail:
BUG: KASAN: vmalloc-out-of-bounds in
tracing_map_destroy_sort_entries+0xa0/0xb0
Read of size 8 at addr ffffc90000045000 by task init/1
tracing_map_destroy_sort_entries+0xa0/0xb0
hist_show+0x6f7/0x1df0
seq_read_iter+0x2b8/0x1190
vfs_read+0x176/0xa40
The buggy address belongs to a 4-page vmalloc region starting at
ffffc90000041000 allocated at tracing_map_sort_entries+0x5c/0xd50
A few pages further the fault is fatal. The registers at the oops confirm
the bound: the loop's end pointer less the array start, over the pointer
size, is 4294967284.
Return the error in a separate variable and leave n_entries holding the
count, the way tracing_map_sort_entries() does on its own error path.
The stats block is only entered for a value carrying .percent or .graph,
which __create_val_field() has rejected since v6.3, so this cannot be
reached in mainline as it stands. It becomes reachable again with
"tracing: hist: let values keep the percent and graph modifiers", so it
should be applied first.
Fixes: abaa5258ce5e ("tracing: Add .percent suffix option to histogram values")
Cc: [email protected]
Signed-off-by: Donggeun Yoo <[email protected]>
---
Reproduced under QEMU x86_64 on 1fc5a74b108f, with the percent/graph patch
applied so the block is reachable and with the stats allocation forced to
fail. Before this change the read of the hist file never returns: KASAN
reports the vmalloc-out-of-bounds quoted above and the kernel then takes a
fatal page fault. After it the read returns, the histogram prints its
header with no rows, and KASAN is silent.
Link:
https://lore.kernel.org/linux-trace-kernel/[email protected]/
kernel/trace/trace_events_hist.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 963e0d6b61fd..67f324d7dc78 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -5690,7 +5690,7 @@ static int print_entries(struct seq_file *m,
{
struct tracing_map_sort_entry **sort_entries = NULL;
struct tracing_map *map = hist_data->map;
- int i, j, n_entries;
+ int i, j, n_entries, ret;
struct hist_val_stat *stats = NULL;
u64 val;
@@ -5700,6 +5700,8 @@ static int print_entries(struct seq_file *m,
if (n_entries < 0)
return n_entries;
+ ret = n_entries;
+
/* Calculate the max and the total for each field if needed. */
for (j = 0; j < hist_data->n_vals; j++) {
if (!(hist_data->fields[j]->flags &
@@ -5708,7 +5710,7 @@ static int print_entries(struct seq_file *m,
if (!stats) {
stats = kzalloc_objs(*stats, hist_data->n_vals);
if (!stats) {
- n_entries = -ENOMEM;
+ ret = -ENOMEM;
goto out;
}
}
@@ -5729,7 +5731,7 @@ static int print_entries(struct seq_file *m,
out:
tracing_map_destroy_sort_entries(sort_entries, n_entries);
- return n_entries;
+ return ret;
}
static void hist_trigger_show(struct seq_file *m,
--
2.53.0
