From f1aa2eb5ea05ccd1fd92d235346e60e90a1ed949 Mon Sep 17 00:00:00 2001 From: Ondrej Mosnacek Date: Fri, 10 Feb 2023 15:58:23 +0100 Subject: sysctl: fix proc_dobool() usability Currently proc_dobool expects a (bool *) in table->data, but sizeof(int) in table->maxsize, because it uses do_proc_dointvec() directly. This is unsafe for at least two reasons: 1. A sysctl table definition may use { .data = &variable, .maxsize = sizeof(variable) }, not realizing that this makes the sysctl unusable (see the Fixes: tag) and that they need to use the completely counterintuitive sizeof(int) instead. 2. proc_dobool() will currently try to parse an array of values if given .maxsize >= 2*sizeof(int), but will try to write values of type bool by offsets of sizeof(int), so it will not work correctly with neither an (int *) nor a (bool *). There is no .maxsize validation to prevent this. Fix this by: 1. Constraining proc_dobool() to allow only one value and .maxsize == sizeof(bool). 2. Wrapping the original struct ctl_table in a temporary one with .data pointing to a local int variable and .maxsize set to sizeof(int) and passing this one to proc_dointvec(), converting the value to/from bool as needed (using proc_dou8vec_minmax() as an example). 3. Extending sysctl_check_table() to enforce proc_dobool() expectations. 4. Fixing the proc_dobool() docstring (it was just copy-pasted from proc_douintvec, apparently...). 5. Converting all existing proc_dobool() users to set .maxsize to sizeof(bool) instead of sizeof(int). Fixes: 83efeeeb3d04 ("tty: Allow TIOCSTI to be disabled") Fixes: a2071573d634 ("sysctl: introduce new proc handler proc_dobool") Signed-off-by: Ondrej Mosnacek Acked-by: Kees Cook Signed-off-by: Luis Chamberlain --- kernel/sysctl.c | 43 ++++++++++++++++++++++++------------------- 1 file changed, 24 insertions(+), 19 deletions(-) (limited to 'kernel/sysctl.c') diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 137d4abe3eda..1c240d2c99bc 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -425,21 +425,6 @@ static void proc_put_char(void **buf, size_t *size, char c) } } -static int do_proc_dobool_conv(bool *negp, unsigned long *lvalp, - int *valp, - int write, void *data) -{ - if (write) { - *(bool *)valp = *lvalp; - } else { - int val = *(bool *)valp; - - *lvalp = (unsigned long)val; - *negp = false; - } - return 0; -} - static int do_proc_dointvec_conv(bool *negp, unsigned long *lvalp, int *valp, int write, void *data) @@ -710,16 +695,36 @@ int do_proc_douintvec(struct ctl_table *table, int write, * @lenp: the size of the user buffer * @ppos: file position * - * Reads/writes up to table->maxlen/sizeof(unsigned int) integer - * values from/to the user buffer, treated as an ASCII string. + * Reads/writes one integer value from/to the user buffer, + * treated as an ASCII string. + * + * table->data must point to a bool variable and table->maxlen must + * be sizeof(bool). * * Returns 0 on success. */ int proc_dobool(struct ctl_table *table, int write, void *buffer, size_t *lenp, loff_t *ppos) { - return do_proc_dointvec(table, write, buffer, lenp, ppos, - do_proc_dobool_conv, NULL); + struct ctl_table tmp; + bool *data = table->data; + int res, val; + + /* Do not support arrays yet. */ + if (table->maxlen != sizeof(bool)) + return -EINVAL; + + tmp = *table; + tmp.maxlen = sizeof(val); + tmp.data = &val; + + val = READ_ONCE(*data); + res = proc_dointvec(&tmp, write, buffer, lenp, ppos); + if (res) + return res; + if (write) + WRITE_ONCE(*data, val); + return 0; } /** -- cgit