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efi_loader: efi_dp_check_length()

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We need to check that device paths provided via UEFI variables are not
malformed.

Provide function efi_dp_check_length() to check if a device path has an
end node within a given number of bytes.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
This commit is contained in:
Heinrich Schuchardt 2020-08-23 10:49:46 +02:00
parent ed0b10722c
commit 5cad4a3093
2 changed files with 35 additions and 0 deletions
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2
include/efi_loader.h
View file

@ -631,6 +631,8 @@ efi_status_t efi_dp_from_name(const char *dev, const char *devnr,
const char *path,
struct efi_device_path **device,
struct efi_device_path **file);
ssize_t efi_dp_check_length(const struct efi_device_path *dp,
const size_t maxlen);
#define EFI_DP_TYPE(_dp, _type, _subtype) \
(((_dp)->type == DEVICE_PATH_TYPE_##_type) && \

33
lib/efi_loader/efi_device_path.c
View file

@ -1127,3 +1127,36 @@ efi_status_t efi_dp_from_name(const char *dev, const char *devnr,
return EFI_SUCCESS;
}
/**
* efi_dp_check_length() - check length of a device path
*
* @dp: pointer to device path
* @maxlen: maximum length of the device path
* Return:
* * length of the device path if it is less or equal @maxlen
* * -1 if the device path is longer then @maxlen
* * -1 if a device path node has a length of less than 4
* * -EINVAL if maxlen exceeds SSIZE_MAX
*/
ssize_t efi_dp_check_length(const struct efi_device_path *dp,
const size_t maxlen)
{
ssize_t ret = 0;
u16 len;
if (maxlen > SSIZE_MAX)
return -EINVAL;
for (;;) {
len = dp->length;
if (len < 4)
return -1;
ret += len;
if (ret > maxlen)
return -1;
if (dp->type == DEVICE_PATH_TYPE_END &&
dp->sub_type == DEVICE_PATH_SUB_TYPE_END)
return ret;
dp = (const struct efi_device_path *)((const u8 *)dp + len);
}
}