linux-kernel - [PATCH] efivars: Respect "block" flag in efivar_entry_set

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Message-Id: <20220218180559.1432559-1-jannh@google.com>
Date:   Fri, 18 Feb 2022 19:05:59 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kees Cook <keescook@...omium.org>, Jann Horn <jannh@...gle.com>
Subject: [PATCH] efivars: Respect "block" flag in efivar_entry_set_safe()

When the "block" flag is false, the old code would sometimes still call
check_var_size(), which wrongly tells ->query_variable_store() that it can
block.

As far as I can tell, this can't really materialize as a bug at the moment,
because ->query_variable_store only does something on X86 with generic EFI,
and in that configuration we always take the efivar_entry_set_nonblocking()
path. So I'm not marking this for stable backporting.

Fixes: ca0e30dcaa53 ("efi: Add nonblocking option to efi_query_variable_store()")
Signed-off-by: Jann Horn <jannh@...gle.com>
---

 drivers/firmware/efi/vars.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
index abdc8a6a3963..cae590bd08f2 100644
--- a/drivers/firmware/efi/vars.c
+++ b/drivers/firmware/efi/vars.c
@@ -742,6 +742,7 @@ int efivar_entry_set_safe(efi_char16_t *name, efi_guid_t vendor, u32 attributes,
 {
 	const struct efivar_operations *ops;
 	efi_status_t status;
+	unsigned long varsize;
 
 	if (!__efivars)
 		return -EINVAL;
@@ -764,15 +765,17 @@ int efivar_entry_set_safe(efi_char16_t *name, efi_guid_t vendor, u32 attributes,
 		return efivar_entry_set_nonblocking(name, vendor, attributes,
 						    size, data);
 
+	varsize = size + ucs2_strsize(name, 1024);
 	if (!block) {
 		if (down_trylock(&efivars_lock))
 			return -EBUSY;
+		status = check_var_size_nonblocking(attributes, varsize);
 	} else {
 		if (down_interruptible(&efivars_lock))
 			return -EINTR;
+		status = check_var_size(attributes, varsize);
 	}
 
-	status = check_var_size(attributes, size + ucs2_strsize(name, 1024));
 	if (status != EFI_SUCCESS) {
 		up(&efivars_lock);
 		return -ENOSPC;

base-commit: 83e396641110663d3c7bb25b9bc0c6a750359ecf
-- 
2.35.1.473.g83b2b277ed-goog