lib/utmp.c: Fix use of last utmp entry instead of patrial-match entry #1327
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This reverts commit 8417765. The pointer returned by getutxent() function may always point to the same shared and reused buffer. Instead of copying the utmp entry pointer value the content of utmp entry must be copied otherwise the next call of getutxent() will overwrite previously found entry. Signed-off-by: Evgeny Grin (Karlson2k) <[email protected]>
Updated utmp entry search algorithm to follow GNU/Linux description: https://man7.org/linux/man-pages/man5/utmp.5.html#DESCRIPTION An entry is found by looking for matching PID. If several such entries found (for example, due to cleanup failure of old entries) then first entry with both matching PID and matching 'ut_line' (current terminal) is used. If not entry has matching 'ut_line' then first entry with matching PID is used (if getty/init process does not set 'ut_line'). When no single entry is matched by PID, then but at least one entry is matched current terminal the the first such entry is selected (if getty does not set correct PID). This commit uses non-portable Elvis operator is it is already used everywhere in the code. Signed-off-by: Evgeny Grin (Karlson2k) <[email protected]>
Instead of using up to three allocation every time when get_current_utmp() function is called, the maximum a single allocation is used. A minor code optimisation is applied: the match by "line" is not checked if entry matched by PID has been already found. Fixes: 8417765 (14-07-2025; "lib/utmp.c: Fix umtp entry search") Signed-off-by: Evgeny Grin (Karlson2k) <[email protected]>
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We merged the alternative implementation without reverting. |
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This is a correction for PR #1292 (and is an alternative version of PR #1326; this PR includes a full revert as the first commit.)
After additional code and documentation analysis I found out that copy of the pointer is not enough, a deep copy must be used instead.
I also checked glibc sources to be absolutely sure.
As allocation is needed for every successful match (either full or partial), I restructured the code to avoid code duplication.
I think this kind of code could be improved with additional comments, as currently it is not fully clear that match by PID has priority over match by line (tty).
Last two commits could be squashed into one commit.