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init/main: fix off-by-one in argv_init cleanup

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Patch series "init: fix array boundary bugs in boot parameter parsing".

This series fixes two distinct boundary logic edge-case bugs in
`init/main.c` related to parsing boot command-line arguments and
environment variables.  Both bugs have been present since the early git
history (Linux-2.6.12-rc2).

1. The first patch fixes an off-by-one error in `init_setup()` where
   the final slot of the `argv_init` array was left uncleared. This
   allowed a stale kernel parameter to leak into the `init` process's
   user-space command line if exactly `MAX_INIT_ARGS` unknown
   parameters were passed.

2. The second patch fixes a false-positive kernel panic in
   `unknown_bootoption()`. If a user filled the environment variable
   array up to its exact limit (32) and then attempted to overwrite
   the final variable, the kernel would panic before evaluating
   whether it was a harmless duplicate.

Exact QEMU reproduction steps for both edge cases are documented inside
their respective commit descriptions.


This patch (of 2):

When cleaning up argv_init in init_setup() and rdinit_setup(), the loop
terminates one element early due to using '<' instead of '<='.  Since
argv_init is sized MAX_INIT_ARGS+2, index MAX_INIT_ARGS is a valid element
that should be cleared to NULL.

If exactly MAX_INIT_ARGS unknown arguments are passed before 'init=', the
uncleared argv_init[MAX_INIT_ARGS] can act as a ghost argument to
/sbin/init or cause a spurious kernel panic when later appended to.

To verify the argument leak, boot a VM into a shell with 32 unknown kernel
arguments, the init parameter, and 31 user arguments:

  STALE_ARGS=$(for i in {1..32}; do echo -n "stale$i "; done)
  USER_ARGS=$(for i in {1..31}; do echo -n "user$i "; done)
  qemu-system-x86_64 -kernel bzImage \
      -append "$STALE_ARGS init=/bin/sh $USER_ARGS"

Running `cat /proc/1/cmdline` inside the shell reveals that the 32nd
kernel argument ('stale32') incorrectly leaked into the init process's
command line.  This patch zeroes the final slot, cleanly terminating the
array.

Link: https://lore.kernel.org/20260818045357.4123784-1-wfelipe@google.com
Link: https://lore.kernel.org/20260818045357.4123784-2-wfelipe@google.com
Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Fixes: ffdfc40976 ("[PATCH] Add rdinit parameter to pick early userspace init")
Signed-off-by: Wilson Felipe Pereira <wfelipe@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Wilson Felipe Pereira 2026-08-18 04:53:46 +00:00 committed by Andrew Morton
parent 456b17ccaa
commit b82ed0e3a1
1 changed files with 2 additions and 2 deletions
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4
init/main.c
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@ -581,7 +581,7 @@ static int __init init_setup(char *str)
* the shell think it should execute a script with such name.
* So we ignore all arguments entered _before_ init=... [MJ]
*/
for (i = 1; i < MAX_INIT_ARGS; i++)
for (i = 1; i <= MAX_INIT_ARGS; i++)
argv_init[i] = NULL;
return 1;
}
@ -594,7 +594,7 @@ static int __init rdinit_setup(char *str)
ramdisk_execute_command = str;
ramdisk_execute_command_set = true;
/* See "auto" comment in init_setup */
for (i = 1; i < MAX_INIT_ARGS; i++)
for (i = 1; i <= MAX_INIT_ARGS; i++)
argv_init[i] = NULL;
return 1;
}