Messages in this thread Patch in this message | | | Date | Fri, 7 Aug 2020 15:18:00 +0200 | From | Jessica Yu <> | Subject | Re: [PATCH 1/2] module: Correctly truncate sysfs sections output |
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+++ Kees Cook [06/08/20 23:35 -0700]: >The only-root-readable /sys/module/$module/sections/$section files >did not truncate their output to the available buffer size. While most >paths into the kernfs read handlers end up using PAGE_SIZE buffers, >it's possible to get there through other paths (e.g. splice, sendfile). >Actually limit the output to the "count" passed into the read function, >and report it back correctly. *sigh* > >Reported-by: kernel test robot <lkp@intel.com> >Link: https://lore.kernel.org/lkml/20200805002015.GE23458@shao2-debian >Fixes: ed66f991bb19 ("module: Refactor section attr into bin attribute") >Cc: stable@vger.kernel.org >Cc: Jessica Yu <jeyu@kernel.org> >Signed-off-by: Kees Cook <keescook@chromium.org>
Oof, thanks for fixing this!
Acked-by: Jessica Yu <jeyu@kernel.org>
>--- > kernel/module.c | 22 +++++++++++++++++++--- > 1 file changed, 19 insertions(+), 3 deletions(-) > >diff --git a/kernel/module.c b/kernel/module.c >index aa183c9ac0a2..08c46084d8cc 100644 >--- a/kernel/module.c >+++ b/kernel/module.c >@@ -1520,18 +1520,34 @@ struct module_sect_attrs { > struct module_sect_attr attrs[]; > }; > >+#define MODULE_SECT_READ_SIZE (3 /* "0x", "\n" */ + (BITS_PER_LONG / 4)) > static ssize_t module_sect_read(struct file *file, struct kobject *kobj, > struct bin_attribute *battr, > char *buf, loff_t pos, size_t count) > { > struct module_sect_attr *sattr = > container_of(battr, struct module_sect_attr, battr); >+ char bounce[MODULE_SECT_READ_SIZE + 1]; >+ size_t wrote; > > if (pos != 0) > return -EINVAL; > >- return sprintf(buf, "0x%px\n", >- kallsyms_show_value(file->f_cred) ? (void *)sattr->address : NULL); >+ /* >+ * Since we're a binary read handler, we must account for the >+ * trailing NUL byte that sprintf will write: if "buf" is >+ * too small to hold the NUL, or the NUL is exactly the last >+ * byte, the read will look like it got truncated by one byte. >+ * Since there is no way to ask sprintf nicely to not write >+ * the NUL, we have to use a bounce buffer. >+ */ >+ wrote = scnprintf(bounce, sizeof(bounce), "0x%px\n", >+ kallsyms_show_value(file->f_cred) >+ ? (void *)sattr->address : NULL); >+ count = min(count, wrote); >+ memcpy(buf, bounce, count); >+ >+ return count; > } > > static void free_sect_attrs(struct module_sect_attrs *sect_attrs) >@@ -1580,7 +1596,7 @@ static void add_sect_attrs(struct module *mod, const struct load_info *info) > goto out; > sect_attrs->nsections++; > sattr->battr.read = module_sect_read; >- sattr->battr.size = 3 /* "0x", "\n" */ + (BITS_PER_LONG / 4); >+ sattr->battr.size = MODULE_SECT_READ_SIZE; > sattr->battr.attr.mode = 0400; > *(gattr++) = &(sattr++)->battr; > } >-- >2.25.1 >
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