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SubjectRe: [PATCH v4] execve.2: execve also returns E2BIG if a string is too long
Hi Rik,

On Wed, Oct 11, 2023 at 12:53:30PM -0400, Rik van Riel wrote:
> Sigh, once again I did a git commit --amend without the latest file change being
> included. The change below should be good. Working with both git and hg gets me sometimes :/
> ---8<---
>
> The execve syscall returns -E2BIG in 3 cases:
> - The total length of the command line arguments and environment is too large.
> - An argument or environment string is longer than MAX_ARG_STRLEN.

I'm still concerned by the wording of this sentence (and the next one).
When I (and any user-space programmer, I think) read "string is longer
than FOO", I read `strlen(string) > FOO`. Since it's rather
`strlen(string) >= FOO`, I think you should clarify. How about this?

- An argument or environment string is longer (including the null byte)
than MAX_ARG_STRLEN.

Thanks,
Alex

> - The full path to the executable exceeds MAX_ARG_STRLEN.
>
> Spell out all 3 cases in the -E2BIG section.
>
> Discovered by moving a too large commandline parameter to an environment
> variable, and finding that things still did not work. Examined the code
> in fs/exec.c to get the details.
>
> This simple shell script starts failing at 2^17 on a system with 4kB
> page size:
> ./exec2big.sh: line 10: /bin/true: Argument list too long
> fork failed at loop 17
>
> STRING="a"
>
> for loop in `seq 20`; do
> STRING="$STRING$STRING"
> export STRING
> if /bin/true ; then
> : # still under the limit
> else
> echo "fork failed at loop $loop"
> fi
> done

Thank you very much!

>
> Signed-off-by: Rik van Riel <riel@surriel.com>
> Suggested-by: Matthew House <mattlloydhouse@gmail.com>
> ---
> man2/execve.2 | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/man2/execve.2 b/man2/execve.2
> index 0d9582492ad1..b689101771e5 100644
> --- a/man2/execve.2
> +++ b/man2/execve.2
> @@ -449,7 +449,12 @@ The total number of bytes in the environment
> .RI ( envp )
> and argument list
> .RI ( argv )
> -is too large.
> +is too large,
> +an argument or environment string is too long,
> +or the full
> +.I pathname
> +of the executable is too long.
> +The terminating NUL is counted as part of the string length.
> .TP
> .B EACCES
> Search permission is denied on a component of the path prefix of
> --
> 2.41.0
>
>

--
<https://www.alejandro-colomar.es/>
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