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basic/efivars: do not return EIO if an efivar read is shorten than fstat size

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On my machine stat returns size 22, but only 20 bytes are read:

openat(AT_FDCWD, "/sys/firmware/efi/efivars/LoaderTimeInitUSec-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f", O_RDONLY|O_NOCTTY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=22, ...}) = 0
read(3, "\6\0\0\0", 4)                  = 4
read(3, "7\0001\0001\0003\0005\0002\0007\0\0\0", 18) = 16
Failed to read LoaderTimeInitUSec: Input/output error

Let's just accept that the kernel is returning inconsistent results.
It seems to happen two only two variables on my machine:
/sys/firmware/efi/efivars/LoaderTimeInitUSec-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f
/sys/firmware/efi/efivars/LoaderTimeMenuUSec-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f
so it might be related to the way we write them.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek 2019-12-06 12:13:34 +01:00
parent a97abb30e7
commit 35b9eb0a72
1 changed files with 7 additions and 6 deletions
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13
src/basic/efivars.c
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@ -90,13 +90,14 @@ int efi_get_variable(
n = read(fd, buf, (size_t) st.st_size - 4); n = read(fd, buf, (size_t) st.st_size - 4);
if (n < 0) if (n < 0)
return -errno; return -errno;
if (n != st.st_size - 4) assert(n <= st.st_size - 4);
return -EIO;
/* Always NUL terminate (2 bytes, to protect UTF-16) */ /* Always NUL terminate (2 bytes, to protect UTF-16) */
((char*) buf)[st.st_size - 4] = 0; ((char*) buf)[n - 4] = 0;
((char*) buf)[st.st_size - 4 + 1] = 0; ((char*) buf)[n - 4 + 1] = 0;
} } else
/* Assume that the reported size is accurate */
n = st.st_size - 4;
/* Note that efivarfs interestingly doesn't require ftruncate() to update an existing EFI variable /* Note that efivarfs interestingly doesn't require ftruncate() to update an existing EFI variable
* with a smaller value. */ * with a smaller value. */
@ -108,7 +109,7 @@ int efi_get_variable(
*ret_value = TAKE_PTR(buf); *ret_value = TAKE_PTR(buf);
if (ret_size) if (ret_size)
*ret_size = (size_t) st.st_size - 4; *ret_size = n;
return 0; return 0;
} }