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    SubjectRe: [PATCH] bpf: replace deprecated strncpy with strscpy
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    On 4/3/24 5:06 AM, Ratheesh Kannoth wrote:
    > On 2024-04-03 at 05:22:50, Justin Stitt (justinstitt@google.com) wrote:
    >> strncpy() is deprecated for use on NUL-terminated destination strings
    >> [1] and as such we should prefer more robust and less ambiguous string
    >> interfaces.
    >>
    >> bpf sym names get looked up and compared/cleaned with various string
    >> apis. This suggests they need to be NUL-terminated (strncpy() suggests
    >> this but does not guarantee it).
    >>
    >> | static int compare_symbol_name(const char *name, char *namebuf)
    >> | {
    >> | cleanup_symbol_name(namebuf);
    >> | return strcmp(name, namebuf);
    >> | }
    >>
    >> | static void cleanup_symbol_name(char *s)
    >> | {
    >> | ...
    >> | res = strstr(s, ".llvm.");
    >> | ...
    >> | }
    >>
    >> Use strscpy() as this method guarantees NUL-termination on the
    >> destination buffer.
    >>
    >> This patch also replaces two uses of strncpy() used in log.c. These are
    >> simple replacements as postfix has been zero-initialized on the stack
    >> and has source arguments with a size less than the destination's size.
    >>
    >> Note that this patch uses the new 2-argument version of strscpy
    >> introduced in Commit e6584c3964f2f ("string: Allow 2-argument
    >> strscpy()").
    >>
    >> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
    >> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
    >> Link: https://github.com/KSPP/linux/issues/90
    >> Cc: linux-hardening@vger.kernel.org
    >> Signed-off-by: Justin Stitt <justinstitt@google.com>
    >> ---
    >> Note: build-tested only.
    >>
    >> Found with: $ rg "strncpy\("
    >> ---
    >> kernel/bpf/core.c | 4 ++--
    >> kernel/bpf/log.c | 4 ++--
    >> 2 files changed, 4 insertions(+), 4 deletions(-)
    >>
    >> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
    >> index 696bc55de8e8..8c9078f4549c 100644
    >> --- a/kernel/bpf/core.c
    >> +++ b/kernel/bpf/core.c
    >> @@ -747,7 +747,7 @@ const char *__bpf_address_lookup(unsigned long addr, unsigned long *size,
    >> unsigned long symbol_start = ksym->start;
    >> unsigned long symbol_end = ksym->end;
    >>
    >> - strncpy(sym, ksym->name, KSYM_NAME_LEN);
    >> + strscpy(sym, ksym->name, KSYM_NAME_LEN);
    > You dont have to check return value of strscpy for errors ?

    That would be overkill, it can be easily audited that both pointers are
    of size KSYM_NAME_LEN, as is the count arg.

    Thanks,
    Daniel

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