* [PATCH] firmware/efi: Add write mutex to prevent uaf - revision
@ 2022-06-07 17:59 Hyunwoo Kim
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From: Hyunwoo Kim @ 2022-06-07 17:59 UTC (permalink / raw)
To: ardb, linux-efi
If the user calls close() in the middle of copy operation in
copy_from_user() of efi_capsule_write(),
the user buffer may be copied to the released page.
This is because ->flush is called unconditionally regardless
of f_count, unlike ->release.
This driver is not a security vulnerability, as only
root privileges can write to it.
However, you need to add a mutex to efi_capsule_write()
and efi_capsule_flush() as root can accidentally break
the page while in use.
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
---
drivers/firmware/efi/capsule-loader.c | 12 ++++++++++++
include/linux/efi.h | 1 +
2 files changed, 13 insertions(+)
diff --git a/drivers/firmware/efi/capsule-loader.c b/drivers/firmware/efi/capsule-loader.c
index 4dde8edd53b6..e50ede51ef38 100644
--- a/drivers/firmware/efi/capsule-loader.c
+++ b/drivers/firmware/efi/capsule-loader.c
@@ -177,6 +177,8 @@ static ssize_t efi_capsule_write(struct file *file, const char __user *buff,
if (count == 0)
return 0;
+ mutex_lock(&cap_info->write_lock);
+
/* Return error while NO_FURTHER_WRITE_ACTION is flagged */
if (cap_info->index < 0)
return -EIO;
@@ -233,12 +235,16 @@ static ssize_t efi_capsule_write(struct file *file, const char __user *buff,
goto failed;
}
+ mutex_unlock(&cap_info->write_lock);
+
return write_byte;
fail_unmap:
kunmap(page);
failed:
efi_free_all_buff_pages(cap_info);
+ mutex_unlock(&cap_info->write_lock);
+
return ret;
}
@@ -256,12 +262,16 @@ static int efi_capsule_flush(struct file *file, fl_owner_t id)
int ret = 0;
struct capsule_info *cap_info = file->private_data;
+ mutex_lock(&cap_info->write_lock);
+
if (cap_info->index > 0) {
pr_err("capsule upload not complete\n");
efi_free_all_buff_pages(cap_info);
ret = -ECANCELED;
}
+ mutex_unlock(&cap_info->write_lock);
+
return ret;
}
@@ -315,6 +325,8 @@ static int efi_capsule_open(struct inode *inode, struct file *file)
return -ENOMEM;
}
+ mutex_init(&cap_info->write_lock);
+
file->private_data = cap_info;
return 0;
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 7d9b0bb47eb3..e274c4e8d7c6 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -204,6 +204,7 @@ struct efi_image_auth {
struct capsule_info {
efi_capsule_header_t header;
efi_capsule_header_t *capsule;
+ struct mutex write_mutex;
int reset_type;
long index;
size_t count;
--
2.25.1
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2022-06-07 17:59 [PATCH] firmware/efi: Add write mutex to prevent uaf - revision Hyunwoo Kim
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