Messages in this thread Patch in this message | | | From | Paul Gortmaker <> | Subject | [PATCH] sched/isolation: don't do unbounded chomp on bootarg string | Date | Sun, 18 Apr 2021 17:54:26 -0400 |
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After commit 3662daf02350 ("sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters") the isolcpus= string is walked to skip over what might be any future flag comma separated additions.
However, there is a logic error, and so as can clearly be seen below, it will ignore its own arg len and search to the end of the bootarg string.
$ dmesg|grep isol Command line: BOOT_IMAGE=/boot/bzImage isolcpus=xyz pleasedontparseme=1 root=/dev/sda1 ro isolcpus: Skipped unknown flag xyz isolcpus: Invalid flag pleasedontparseme=1 root=/dev/sda1 ro
This happens because the flag "skip" code does an unconditional increment, which skips over the '\0' check the loop body looks for. If the isolcpus= happens to be the last bootarg, then you'd never notice?
So we only increment if the skipped flag is followed by a comma, as per what the existing "continue" flag matching code does.
Note that isolcpus= was declared deprecated as of v4.15 (b0d40d2b22fe), so we might want to revisit that if we are trying to future-proof it as recently as a year ago for as yet unseen new flags.
Cc: Peter Xu <peterx@redhat.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Frederic Weisbecker <frederic@kernel.org> Fixes: 3662daf02350 ("sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters") Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c index 5a6ea03f9882..9652dba7e938 100644 --- a/kernel/sched/isolation.c +++ b/kernel/sched/isolation.c @@ -188,7 +188,8 @@ static int __init housekeeping_isolcpus_setup(char *str) } pr_info("isolcpus: Skipped unknown flag %.*s\n", len, par); - str++; + if (str[1] == ',') /* above continue; match on "flag," */ + str++; } /* Default behaviour for isolcpus without flags */ -- 2.25.1
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