On Tue, 5 Aug 2025 15:12:03 +0000 Pu Lehui <[email protected]> wrote:
> From: Pu Lehui <[email protected]> > > When the length of the string written to set_ftrace_filter exceeds > FTRACE_BUFF_MAX, the following KASAN alarm will be triggered: > > BUG: KASAN: slab-out-of-bounds in strsep+0x18c/0x1b0 > Read of size 1 at addr ffff0000d00bd5ba by task ash/165 > > CPU: 1 UID: 0 PID: 165 Comm: ash Not tainted 6.16.0-g6bcdbd62bd56-dirty #3 > NONE > Hardware name: linux,dummy-virt (DT) > Call trace: > show_stack+0x34/0x50 (C) > dump_stack_lvl+0xa0/0x158 > print_address_description.constprop.0+0x88/0x398 > print_report+0xb0/0x280 > kasan_report+0xa4/0xf0 > __asan_report_load1_noabort+0x20/0x30 > strsep+0x18c/0x1b0 > ftrace_process_regex.isra.0+0x100/0x2d8 > ftrace_regex_release+0x484/0x618 > __fput+0x364/0xa58 > ____fput+0x28/0x40 > task_work_run+0x154/0x278 > do_notify_resume+0x1f0/0x220 > el0_svc+0xec/0xf0 > el0t_64_sync_handler+0xa0/0xe8 > el0t_64_sync+0x1ac/0x1b0 > > The reason is that trace_get_user will fail when processing a string > longer than FTRACE_BUFF_MAX, but not set the end of parser->buffer > to 0. Then an oob access will be triggered in ftrace_regex_release-> > ftrace_process_regex->strsep->strpbrk. We can solve this problem by > zero-initializing parser->buffer. > > Fixes: 8c9af478c06b ("ftrace: Handle commands when closing set_ftrace_filter > file") Fix one bug then create another!!! > Signed-off-by: Pu Lehui <[email protected]> > --- > kernel/trace/trace.c | 5 +---- > 1 file changed, 1 insertion(+), 4 deletions(-) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index 4283ed4e8f59..97e66cbd3617 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -1776,7 +1776,7 @@ int trace_parser_get_init(struct trace_parser *parser, > int size) > { > memset(parser, 0, sizeof(*parser)); > > - parser->buffer = kmalloc(size, GFP_KERNEL); > + parser->buffer = kzalloc(size, GFP_KERNEL); > if (!parser->buffer) > return 1; > > @@ -1860,13 +1860,10 @@ int trace_get_user(struct trace_parser *parser, const > char __user *ubuf, > > /* We either got finished input or we have to wait for another call. */ > if (isspace(ch) || !ch) { > - parser->buffer[parser->idx] = 0; > parser->cont = false; > } else if (parser->idx < parser->size - 1) { > parser->cont = true; > parser->buffer[parser->idx++] = ch; > - /* Make sure the parsed string always terminates with '\0'. */ > - parser->buffer[parser->idx] = 0; The returned buffer is expected to end with a '0'. This now removes that if the idx is the length of the parser. > } else { > return -EINVAL; > } The real fix would be: diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index d0b1964648c1..422224a55f1d 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -815,7 +815,7 @@ int trace_pid_write(struct trace_pid_list *filtered_pids, loff_t pos; pid_t pid; - if (trace_parser_get_init(&parser, PID_BUF_SIZE + 1)) + if (trace_parser_get_init(&parser, PID_BUF_SIZE)) return -ENOMEM; /* @@ -1776,7 +1776,7 @@ int trace_parser_get_init(struct trace_parser *parser, int size) { memset(parser, 0, sizeof(*parser)); - parser->buffer = kmalloc(size, GFP_KERNEL); + parser->buffer = kmalloc(size + 1, GFP_KERNEL); if (!parser->buffer) return 1; diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index 05447b958a1a..a3ce88a48947 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -1507,7 +1507,7 @@ ftrace_event_write(struct file *file, const char __user *ubuf, if (ret < 0) return ret; - if (trace_parser_get_init(&parser, EVENT_BUF_SIZE + 1)) + if (trace_parser_get_init(&parser, EVENT_BUF_SIZE)) return -ENOMEM; read = trace_get_user(&parser, ubuf, cnt, ppos); -- Steve
