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author | Lennart Poettering <lennart@poettering.net> | 2021-09-16 12:20:09 +0200 |
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committer | Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl> | 2021-10-12 17:04:34 +0200 |
commit | c9e0daf821b3e1e6504ca4c4e3a8b73513e28fa7 (patch) | |
tree | 0d88eb1d9936ea950119dd5dd4f78f61736bcaff | |
parent | b3f5d2f4044751a4a741e033a9bc621ede573cb2 (diff) | |
download | systemd-c9e0daf821b3e1e6504ca4c4e3a8b73513e28fa7.tar.gz |
fileio: fix truncated read handling in read_virtual_file()
We mishandled the case where the size we read from the file actually
matched the maximum size fully. In that case we cannot really make a
determination whether the file was fully read or only partially. In that
case let's do another loop, so that we operate with a buffer, and
we can detect the EOF (which will be signalled to us via a short read).
(cherry picked from commit 00bd9a4a82ed57bc0c7f158da4564fc1eab808b4)
-rw-r--r-- | src/basic/fileio.c | 11 |
1 files changed, 8 insertions, 3 deletions
diff --git a/src/basic/fileio.c b/src/basic/fileio.c index 1046e5b9b4..6c8ebe63e0 100644 --- a/src/basic/fileio.c +++ b/src/basic/fileio.c @@ -470,9 +470,14 @@ int read_virtual_file(const char *filename, size_t max_size, char **ret_contents if (n <= size) break; - /* If a maximum size is specified and we already read as much, no need to try again */ - if (max_size != SIZE_MAX && n >= max_size) { - n = max_size; + /* If a maximum size is specified and we already read more we know the file is larger, and + * can handle this as truncation case. Note that if the size of what we read equals the + * maximum size then this doesn't mean truncation, the file might or might not end on that + * byte. We need to rerun the loop in that case, with a larger buffer size, so that we read + * at least one more byte to be able to distinguish EOF from truncation. */ + if (max_size != SIZE_MAX && n > max_size) { + n = size; /* Make sure we never use more than what we sized the buffer for (so that + * we have one free byte in it for the trailing NUL we add below).*/ truncated = true; break; } |