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UBUNTU: SAUCE: arm64: v6.8: cmdline param >= 146 chars kills kernel

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BugLink: https://bugs.launchpad.net/bugs/2069534

This is v6.8 specific; v6.9 is reported as not affected (due to
extensive code refactoring).

Commit dc3f5aae06 reworked how early cmdline CPU feature parsing
is done, and converted to using memcmp() in preparation for the move to
the pi minimal C standard library.
As a result it caused a regression where-by a parameter >= 146
characters on the kernel command line would cause a silent panic with no
console clues as to why.
It is due to memcmp() in include/linux/fortify-string.h detecting an
attempted out-of-bounds read. The cause itself is subtle.

arch/arm64/kernel/idreg-override.c::__parse_cmdline() compares the
struct aliases entries with each parameter via memcmp().

...
static const struct {
char alias[FTR_ALIAS_NAME_LEN];
char feature[FTR_ALIAS_OPTION_LEN];
} aliases[]

Each element is 146 characters. When a parameter is also 146 characters
the call looks like memcmp(buf, aliases[i].alias, len+1) where len is
the equivalent of strlen(buf) and +1 to compare including the trailing
NUL.

That triggers the fortified memcmp()'s:

if (p_size < size || q_size < size)
fortify_panic(__func__);

where q_size == 146, size == 147

The solution here is to not call memcmp() at all unless the two strings
have the same length.

Initially reported in Ubuntu (and confirmed to affect Debian and
Mainline):

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2069534

Fixes: dc3f5aae06 ("arm64: idreg-override: Avoid parameq() and parameqn()")
Signed-off-by: Tj <tj.iam.tj@proton.me>
Signed-off-by: Matthew Ruffell <matthew.ruffell@canonical.com>
Acked-by: Roxana Nicolescu <roxana.nicolescu@canonical.com>
Acked-by: Manuel Diewald <manuel.diewald@canonical.com>
Signed-off-by: Manuel Diewald <manuel.diewald@canonical.com>
Signed-off-by: Roxana Nicolescu <roxana.nicolescu@canonical.com>
This commit is contained in:
Tj
2024-07-30 11:28:38 +12:00
committed by Roxana Nicolescu
parent 7674328e5c
commit c681536471
1 changed files with 2 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files
arch/arm64/kernel/idreg-override.c
+2 -1
View File
@@ -308,7 +308,8 @@ static __init void __parse_cmdline(const char *cmdline, bool parse_aliases)
match_options(buf);
for (i = 0; parse_aliases && i < ARRAY_SIZE(aliases); i++)
if (!memcmp(buf, aliases[i].alias, len + 1))
if (len == strlen(aliases[i].alias) &&
!memcmp(buf, aliases[i].alias, len + 1))
__parse_cmdline(aliases[i].feature, false);
} while (1);
}