imgact_elf: Fix off-by-one in note size check

Prior to c86af2cc4cd1 ("imgact_elf: Check note body sizes"), this was
note_name + n_namesz >= note_end, which checks that there is at least
one byte after the unpadded name (which could be either padding or
data), and given our notes always have data with them this was fine.
However, once we started checking the padded name (note that "FreeBSD\0"
is already a multiple of 4 bytes, so has no padding) and data, this
turned into checking that there is at least one byte after the unpadded
data, and since our ELF notes already have a multiple of 4 bytes for
their data and therefore have no padding, this means that we are now
checking that there is at least one byte after the ELF note, which is
not going to be the case for the last ELF note. Instead, switch this to
a strict greater than, as should be used when comparing one-past-the-end
pointers, which both sides of the inequality are.

For executables, this was generally not a problem in reality, since the
last of our ELF notes is NT_FREEBSD_NOINIT_TAG, which isn't read by the
kernel. However, ld-elf.so.1 (and libcompat variants), like shared
libraries, only has NT_FREEBSD_ABI_TAG, which meant the kernel did not
see this ELF note when directly executing it (e.g. as done by ldd), and
on RISC-V this is the only branding present, so doing so would fail with
ENOEXEC. This does also mean on non-RISC-V direct exec ld-elf.so.1 runs
with the wrong p_osrel, but given it sets kern.proc.osrel.PID to the
executable's NT_FREEBSD_ABI_TAG that it loads, this probably doesn't
matter in practice.

PR:		291446
Reported by:	bdragon
Tested by:	bdragon
Fixes:		c86af2cc4cd1 ("imgact_elf: Check note body sizes")
MFC after:	3 days

1 files changed, 1 insertions, 1 deletions

diff --git a/sys/kern/imgact_elf.c b/sys/kern/imgact_elf.c
index 779158b41221..f1d848e95f18 100644
--- a/sys/kern/imgact_elf.c
+++ b/sys/kern/imgact_elf.c
@@ -2840,7 +2840,7 @@ __elfN(parse_notes)(const struct image_params *imgp, const Elf_Note *checknote,
 			goto nextnote;
 		note_name = (const char *)(note + 1);
 		if (note_name + roundup2(note->n_namesz, ELF_NOTE_ROUNDSIZE) +
-		    note->n_descsz >= (const char *)note_end ||
+		    note->n_descsz > (const char *)note_end ||
 		    strncmp(note_vendor, note_name, checknote->n_namesz) != 0)
 			goto nextnote;