[LTP] [PATCH v3] read_all: Fix buffer too small for long paths

[LTP] [PATCH v3] read_all: Fix buffer too small for long paths

[Michael Menasherov via ltp]

queue_pop() copies each path into popped[BUFFER_SIZE], but BUFFER_SIZE
was 1024 while visit_dir() builds paths up to PATH_MAX. Any path longer
than 1023 bytes aborted the test with TBROK.

Use PATH_MAX for BUFFER_SIZE and MAX_PATH, and drop the extra -1 from
the queue_pop() bound so a PATH_MAX - 1 character path fits.

Tested on smaller boards and then on local machines with deeply nested
directories under /sys.

Fixes: 67c95fbbfc3a ("Add read_all file systems test")
Signed-off-by: Michael Menasherov <mmenashe@redhat.com>
---
 testcases/kernel/fs/read_all/read_all.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/testcases/kernel/fs/read_all/read_all.c b/testcases/kernel/fs/read_all/read_all.c
index 5720ffb99..ec9454fc9 100644
--- a/testcases/kernel/fs/read_all/read_all.c
+++ b/testcases/kernel/fs/read_all/read_all.c
@@ -51,8 +51,8 @@
 #include "tst_timer.h"
 
 #define QUEUE_SIZE 16384
-#define BUFFER_SIZE 1024
-#define MAX_PATH 4096
+#define BUFFER_SIZE PATH_MAX
+#define MAX_PATH PATH_MAX
 #define MAX_DISPLAY 40
 
 struct queue {
@@ -131,7 +131,7 @@ static int queue_pop(struct queue *q)
 	while (q->data[i]) {
 		q->popped[j] = q->data[i];
 
-		if (++j >= BUFFER_SIZE - 1)
+		if (++j >= BUFFER_SIZE)
 			tst_brk(TBROK, "Buffer is too small for path");
 
 		 i = (i + 1) % QUEUE_SIZE;
-- 
2.55.0


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Re: [LTP] read_all: Fix buffer too small for long paths

[linuxtestproject.agent]

Hi Michael,

On Tue Sep 8 12:22:48 2026 +0300, Michael Menasherov via ltp wrote:
> read_all: Fix buffer too small for long paths

Verdict - Reviewed

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Note:

The agent can sometimes produce false positives although often its
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comment this email or ignore the suggestions.

Regards,
LTP AI Reviewer

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Re: [LTP] [PATCH v3] read_all: Fix buffer too small for long paths

[Andrea Cervesato via ltp]

Reviewed-by: Andrea Cervesato <andrea.cervesato@suse.com>

--
Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com

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Re: [LTP] [PATCH v3] read_all: Fix buffer too small for long paths

[Cyril Hrubis]

Hi!
> diff --git a/testcases/kernel/fs/read_all/read_all.c b/testcases/kernel/fs/read_all/read_all.c
> index 5720ffb99..ec9454fc9 100644
> --- a/testcases/kernel/fs/read_all/read_all.c
> +++ b/testcases/kernel/fs/read_all/read_all.c
> @@ -51,8 +51,8 @@
>  #include "tst_timer.h"
>  
>  #define QUEUE_SIZE 16384
> -#define BUFFER_SIZE 1024
> -#define MAX_PATH 4096
> +#define BUFFER_SIZE PATH_MAX
> +#define MAX_PATH PATH_MAX
>  #define MAX_DISPLAY 40

This part looks good.

>  struct queue {
> @@ -131,7 +131,7 @@ static int queue_pop(struct queue *q)
>  	while (q->data[i]) {
>  		q->popped[j] = q->data[i];
>  
> -		if (++j >= BUFFER_SIZE - 1)
> +		if (++j >= BUFFER_SIZE)
>  			tst_brk(TBROK, "Buffer is too small for path");
>  
>  		 i = (i + 1) % QUEUE_SIZE;

However here we do:

q->popped[j] = '\0';

So j must be at most BUFFER_SIZE-1 and with the change above j may end
up equal to BUFFER_SIZE and we will land off by one in the array.

-- 
Cyril Hrubis
chrubis@suse.cz

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Re: [LTP] [PATCH v3] read_all: Fix buffer too small for long paths

[Michael Menasherov via ltp]

Hi Cyril
Thanks for explaining the problem with the code. I took a better look at it.
How about checking before the write instead:

      while (q->data[i]) {
          if (j >= BUFFER_SIZE - 1)
              tst_brk(TBROK, "Buffer is too small for path");

          q->popped[j++] = q->data[i];
          i = (i + 1) % QUEUE_SIZE;
      }
      q->popped[j] = '\0';

  j can never reach BUFFER_SIZE without TBROK, and PATH_MAX - 1 paths
  still fit. Does this look good to you?

  Thanks,
  Michael Menasherov.

On Tue, Sep 15, 2026 at 3:57 PM Cyril Hrubis <chrubis@suse.cz> wrote:

> Hi!
> > diff --git a/testcases/kernel/fs/read_all/read_all.c
> b/testcases/kernel/fs/read_all/read_all.c
> > index 5720ffb99..ec9454fc9 100644
> > --- a/testcases/kernel/fs/read_all/read_all.c
> > +++ b/testcases/kernel/fs/read_all/read_all.c
> > @@ -51,8 +51,8 @@
> >  #include "tst_timer.h"
> >
> >  #define QUEUE_SIZE 16384
> > -#define BUFFER_SIZE 1024
> > -#define MAX_PATH 4096
> > +#define BUFFER_SIZE PATH_MAX
> > +#define MAX_PATH PATH_MAX
> >  #define MAX_DISPLAY 40
>
> This part looks good.
>
> >  struct queue {
> > @@ -131,7 +131,7 @@ static int queue_pop(struct queue *q)
> >       while (q->data[i]) {
> >               q->popped[j] = q->data[i];
> >
> > -             if (++j >= BUFFER_SIZE - 1)
> > +             if (++j >= BUFFER_SIZE)
> >                       tst_brk(TBROK, "Buffer is too small for path");
> >
> >                i = (i + 1) % QUEUE_SIZE;
>
> However here we do:
>
> q->popped[j] = '\0';
>
> So j must be at most BUFFER_SIZE-1 and with the change above j may end
> up equal to BUFFER_SIZE and we will land off by one in the array.
>
> --
> Cyril Hrubis
> chrubis@suse.cz
>
>

-- 

Michael Menasherov

Software Quality Engineer - Automotive Kernel

Red Hat <https://www.redhat.com/>
<https://www.redhat.com/>

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Re: [LTP] [PATCH v3] read_all: Fix buffer too small for long paths

[Cyril Hrubis]

Hi!
> Thanks for explaining the problem with the code. I took a better look at it.
> How about checking before the write instead:
> 
>       while (q->data[i]) {
>           if (j >= BUFFER_SIZE - 1)
>               tst_brk(TBROK, "Buffer is too small for path");
> 
>           q->popped[j++] = q->data[i];
>           i = (i + 1) % QUEUE_SIZE;
>       }
>       q->popped[j] = '\0';
> 
>   j can never reach BUFFER_SIZE without TBROK, and PATH_MAX - 1 paths
>   still fit. Does this look good to you?

Ah, righ, there is tst_brk(), sorry for missing that.

-- 
Cyril Hrubis
chrubis@suse.cz

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Re: [LTP] [PATCH v3] read_all: Fix buffer too small for long paths

[Cyril Hrubis]

Hi!
Pushed, thanks.

-- 
Cyril Hrubis
chrubis@suse.cz

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